OFFSET
1,2
COMMENTS
Partial sums of A263477.
LINKS
Hiroaki Yamanouchi, Table of n, a(n) for n = 1..50
Eric Weisstein's World of Mathematics, Multiplicative Digital Root
FORMULA
MATHEMATICA
Length@ Select[Range[10^# - 1], FixedPoint[Times @@ IntegerDigits@ # &, #] == 2 &] & /@ Range@ 6 (* Michael De Vlieger, Oct 19 2015 *)
PROG
(PARI) t(k) = {while(k>9, k=prod(i=1, #k=digits(k), k[i])); k}
a(n) = sum(i=1, 10^n - 1, if(t(i) == 2, 1, 0)); \\ Altug Alkan, Oct 19 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Martin Renner, Oct 19 2015
EXTENSIONS
a(8) from Michael De Vlieger, Oct 19 2015
a(9)-a(23) from Hiroaki Yamanouchi, Oct 25 2015
STATUS
approved