0,2

Probably finite sequence. The multiplicative persistence of a number is the number of times you need to multiply the digits together before reaching a single digit.

Table of n, a(n) for n=0..11.

For n=4, a(4) = 39 because 39 is the smallest nonprime number with multiplicative persistence 3: 39 -> 27 -> 14 -> 4.

Cf. A046500 (smallest prime with multiplicative persistence n).

Sequence in context: A087473 A014120 A003001 * A038350 A003344 A047721

Adjacent sequences: A198374 A198375 A198376 * A198378 A198379 A198380

nonn,base

Jaroslav Krizek, Oct 23 2011

approved