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 A354618 #24 Jul 11 2022 16:04:54
%S A354618 0,3,3,0,6,6,9,12,12,18,33,24,9,3,12,18,33,42,45,30,30,36,42,33,45,48,
%T A354618 39,54,42,42,54,57,48,27,42,33,45,48,57,63,69,87,99,93,93,54,42,60,72,
%U A354618 93,75,72,51,42,45,75,111,135,141,114,117,120,102,81,78,78
%N A354618 a(n) = (sum of the digits of 5^n) - (sum of the digits of 2^n).
%C A354618 Wu Wei Chao asked in American Mathematical Monthly for a proof that a(n) >= 0 with a(n) = 0 only if n = 0 or n = 3 (see Richard K. Guy reference).
%D A354618 Richard K. Guy, Unsolved Problems in Number Theory, 3rd Edition, Springer, 2004, Section F24, Some decimal digital problems, p. 398.
%F A354618 a(n) = A066001(n) - A001370(n).
%e A354618 a(6) = sod(5^6) - sod(2^6) = sod(15625) - sod(64) = (1+5+6+2+5) - (6+4) = 19 - 10 = 9.
%t A354618 a[n_] := Subtract @@ (Plus @@ IntegerDigits[#] & /@ {5^n, 2^n}); Array[a, 100, 0] (* _Amiram Eldar_, Jul 09 2022 *)
%o A354618 (PARI) a(n) = sumdigits(5^n) - sumdigits(2^n); \\ _Michel Marcus_, Jul 09 2022
%o A354618 (Python)
%o A354618 def a(n): return sum(map(int, str(5**n))) - sum(map(int, str(2**n)))
%o A354618 print([a(n) for n in range(66)]) # _Michael S. Branicky_, Jul 09 2022
%Y A354618 Cf. A001370, A007953, A066001.
%K A354618 nonn,base
%O A354618 0,2
%A A354618 _Bernard Schott_, Jul 08 2022