Number Formulas

Convert a number into currency format	Number - Convert
Convert a number into words	Number - Convert
Return a list of random numbers in a particular range	Other - Other
Return a number reduced by 10 percent	Number - Return
Return numbers to the nearest fraction	Number - Display
Return random numbers in a particular range	Number - Return
Return the decimal part of a number	Number - Return
Return the digits in reverse order	Number - Return
Return the integer part of a number	Number - Return
Return the percentage change	Number - Display
Round a number down	Number - Round
Round a number down to the nearest 100	Number - Round
Round a number down to the nearest 5	Number - Round
Round a number down to the nearest multiple	Number - Round
Round a number to n significant figures	Number - Round
Round a number up	Number - Round
Round a number up to the nearest 100	Number - Round
Round a number up to the nearest 5	Number - Round
Round a number up to the nearest multiple	Number - Round
Test if a number is prime	Conditional - If

Convert a number into currency format Number - Convert
Convert a number into words Number - Convert
Return a list of random numbers in a particular range Other - Other
Return a number reduced by 10 percent Number - Return
Return numbers to the nearest fraction Number - Display
Return random numbers in a particular range Number - Return
Return the decimal part of a number Number - Return
Return the digits in reverse order Number - Return
Return the integer part of a number Number - Return
Return the percentage change Number - Display
Round a number down Number - Round
Round a number down to the nearest 100 Number - Round
Round a number down to the nearest 5 Number - Round
Round a number down to the nearest multiple Number - Round
Round a number to n significant figures Number - Round
Round a number up Number - Round
Round a number up to the nearest 100 Number - Round
Round a number up to the nearest 5 Number - Round
Round a number up to the nearest multiple Number - Round
Test if a number is prime Conditional - If

Convert a number into currency format

	A
1	=TEXT(A1,"£#,##0.00")

Convert a number into words

This user defined function can return the word equivalent for a numerical value.

	A
1	??

SPELLNUMBER - Returns the text after converting a number into words.

Return a number reduced by 10 percent

	A
1	??

To decrease all the values in a range by 10 percent, type 0.9 into a cell, copy the cell and select the range. (Edit > Paste Special) Select Multiply.

Return numbers to the nearest fraction

	A	B
1	12.485	4.26
2	12.3	74.2
3	12.29	123.456
4	=ROUND(A1/0.2, 0)*0.2 = 12.4
5	=ROUND(A2/0.2, 0)*0.2 = 12.4
6	=ROUND(A3/0.2, 0)*0.2 = 12.2
7	=ROUND(B1/0.5, 0)*0.5 = 4.5
8	=ROUND(B2/50, 0)*50 = 50
9	=ROUND(B3/25, 0)*25 = 125

A4 - (rounded down)
A5 - (rounded up)
A6 - (rounded down)
A7 - (rounded up)
A8 - (rounded down)
A9 - (rounded up)
ROUND

Return the digits in reverse order

	A
1	87654321
2	=RIGHT(SUM(VALUE(MID(A1&"1", ROW(INDIRECT("1:"&LEN(A1&"1"))), 1))10^(ROW(INDIRECT("1:"&LEN(A1&"1")))-1)), LEN*(A1)) = 12345678
3
4	101010
5	=RIGHT(SUM(VALUE(MID(A4&"1", ROW(INDIRECT("1:"&LEN(A4&"1"))), 1))10^(ROW(INDIRECT("1:"&LEN(A4&"1")))-1)), LEN*(A4)) = 10101
6
7	1234567890123450
8	=RIGHT(SUM(VALUE(MID(A7&"1", ROW(INDIRECT("1:"&LEN(A7&"1"))), 1))10^(ROW(INDIRECT("1:"&LEN(A7&"1")))-1)), LEN*(A7)) = 0543210987654300
9
10	1234567890123456789
11	=RIGHT(SUMPRODUCT(VALUE(MID(A10&"1", ROW(INDIRECT("1:"&LEN(A10&"1"))), 1))10^(ROW(INDIRECT("1:"&LEN(A10&"1")))-1)), LEN*(A10)) = 9876543210987700000
12
13	11111000000000000000000000000000
14	=RIGHT(SUM(VALUE(MID(A13&"1", ROW(INDIRECT("1:"&LEN(A13&"1"))), 1))10^(ROW(INDIRECT("1:"&LEN(A13&"1")))-1)), LEN*(A13)) = 1E+32

You can return the digits of a number (that has less than 15 digits) in reverse order by using an array formula.
This formula returns a text value (left aligned) to allow for any numbers that end with a zero.
This formula must be entered as an array formula using (Ctrl + Shift + Enter).
1 - Contains the number 87,654,321.
2 - Contains the array formula that reverses these digits.
4 - Contains the binary number 101010.
5 - Contains the array formula that reverses these digits. Notice that it has removed the zero from the front.
7 - Contains a number that has more than 15 digits.
8 - Contains the array formula that tries to reverse these digits. Notice that some rounding has taken place and that this is not exactly the same number.
If you want to reverse more than 15 digits then you will need to use the REVERSE Custom Function.
REVERSE - Returns the contents of a cell with all the characters reversed.

Test if a number is prime

	A
1	=IF(C9=2,"Prime",IF(AND(MOD(C9,ROW(INDIRECT("2:"&ROUNDUP(SQRT(C9),0))))<>0),"Prime","Not Prime"))

This is an array formula. Therefore, you must press CTRL SHIFT ENTER after entering the formula and whenever you edit it later.
You must enter the test number in cell C9.