OFFSET
0,2
COMMENTS
We can expect and conjecture that a(n) ~ 4.5*log_10(5)*n, but for n ~ 10^3..10^4 there are still fluctuations of +- 1%, e.g., a(10^3)/log_10(5) ~ 4538, a(10^4)/log_10(5) ~ 44518. Modulo 9, the sequence is periodic with period (1, 5, 7, 8, 4, 2) of length 6. No term is divisible by 3, a(n) = (-1)^n (mod 3). - M. F. Hasler, May 18 2017
LINKS
Harry J. Smith, Table of n, a(n) for n = 0..1000
MATHEMATICA
Table[ Total@ IntegerDigits[5^n], {n, 0, 60}] (* Robert G. Wilson v Oct 25 2006 *).
Table[Total[IntegerDigits[5^n]], {n, 0, 60}] (* Vincenzo Librandi, Oct 08 2013 *)
PROG
(PARI) SumD(x)= { local(s=0); while (x>9, s+=x%10; x\=10); return(s + x) } { for (n=0, 1000, a=SumD(5^n); write("b066001.txt", n, " ", a) ) } \\ Harry J. Smith, Nov 06 2009
(PARI) A066001=a(n)=sumdigits(5^n); \\ Michel Marcus, Sep 04 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Dec 11 2001
STATUS
approved