If the number is n, then when multiplied by itself four times we write n^4, which is usually printed as n with a small number 4 as a superscript (a number placed to the right of n but positioned a little higher than it). The product of a number and a symbol like x, n, y, etc., is not usually shown with a multiply sign (*) but is written immediately before the symbol, so 15n means 15*n. When we combine as a product 15 and n^4 we get 15n^4.