This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A066001 #33 Aug 05 2025 07:50:35
%S A066001 1,5,7,8,13,11,19,23,25,26,40,38,28,23,34,44,58,56,64,59,61,62,67,74,
%T A066001 82,77,79,89,85,83,91,104,106,89,103,92,109,104,124,134,130,137,145,
%U A066001 149,151,116,112,128,145,158,151,152,130,119,127,167,196,215,211,191
%N A066001 Sum of digits of 5^n.
%C A066001 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
%H A066001 Harry J. Smith, <a href="/A066001/b066001.txt">Table of n, a(n) for n = 0..1000</a>
%F A066001 a(n) = A007953(A000351(n)). - _Michel Marcus_, Aug 05 2025
%t A066001 Table[ Total@ IntegerDigits[5^n], {n, 0, 60}] (* _Robert G. Wilson v_, Oct 25 2006 *)
%t A066001 Table[Total[IntegerDigits[5^n]], {n, 0, 60}] (* _Vincenzo Librandi_, Oct 08 2013 *)
%o A066001 (PARI) a(n)=sumdigits(5^n); \\ _Michel Marcus_, Sep 04 2014
%Y A066001 Cf. A007953, A000351.
%Y A066001 Cf. sum of digits of k^n: A001370 (k=2), A004166 (k=3), A065713 (k=4), this sequence (k=5), A066002 (k=6), A066003 (k=7), A066004 (k=8), A065999 (k=9), A066005 (k=11), A066006 (k=12), A175527 (k=13).
%K A066001 nonn,base
%O A066001 0,2
%A A066001 _N. J. A. Sloane_, Dec 11 2001