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 A366922 #18 Oct 29 2023 14:58:08 %S A366922 2,2,3,2,2,3,2,2,4,2,2,3,2,2,3,2,2,4,2,2,3,2,2,3,2,2,5,2,2,3,2,2,3,2, %T A366922 2,4,2,2,3,2,2,3,2,2,4,2,2,3,2,2,3,2,2,5,2,2,3,2,2,3,2,2,4,2,2,3,2,2, %U A366922 3,2,2,4,2,2,3,2,2,3,2,2,6,2,2,3,2,2,3,2,2,4 %N A366922 a(n) is the exponent of 3 in the prime factorization of 10^n - 1. %C A366922 1 %F A366922 a(n) = A007949(10^n - 1). %F A366922 a(n) = A007949(n) + 2 = A051064(n) + 1. %t A366922 a[n_]:=IntegerExponent[10^n-1,3]; Array[a,90] (* _Stefano Spezia_, Oct 28 2023 *) %o A366922 (PARI) a366922(n) = valuation(10^n-1,3) %o A366922 (Python) %o A366922 def A366922(n): %o A366922 c = 0 %o A366922 a, b = divmod(10**n-1, 3) %o A366922 while b == 0: %o A366922 a, b = divmod(a, 3) %o A366922 c += 1 %o A366922 return c # _Chai Wah Wu_, Oct 29 2023 %Y A366922 Cf. A002283, A003020, A007949, A051064, A057951, A102347, A366921. %K A366922 nonn,easy %O A366922 1,1 %A A366922 _Hugo Pfoertner_, Oct 28 2023