OFFSET
0,26
COMMENTS
Coincides with A031346 up to n=204.
Differs from A087472 first at n=110. - R. J. Mathar, Aug 10 2020
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, E16, pages 262-263.
LINKS
Lucas Colucci, Table of n, a(n) for n = 0..9999
Gabriel Bonuccelli, Lucas Colucci, and Edson de Faria, On the Erdős-Sloane and Shifted Sloane Persistence, arXiv:2009.01114 [math.NT], 2020.
MAPLE
A335808 := proc(n)
option remember;
if n < 10 then
0 ;
elif n < 20 then
1 ;
else
A051801(n) ;
1+procname(%) ;
end if;
end proc: # R. J. Mathar, Aug 10 2020
MATHEMATICA
Array[-1 + Length[NestWhileList[Times @@ DeleteCases[IntegerDigits[#], _?(# == 0 &)] &, #, # >= 10 &]] &, 105, 0] (* Michael De Vlieger, Jun 24 2020 *)
PROG
(PARI) a(n) = for (k=0, oo, if (n<10, return (k), n=vecprod(select(sign, digits(n))))) \\ Rémy Sigrist, Jul 18 2020
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Lucas Colucci, Jun 24 2020
STATUS
approved