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 A371638 #16 Mar 31 2024 11:41:06 %S A371638 2,4,7,8,10,13,14,16,20,20,22,25,26,28,31,32,34,38,38,40,43,44,46,49, %T A371638 50,52,57,56,58,61,62,64,67,68,70,74,74,76,79,80,82,85,86,88,92,92,94, %U A371638 97,98,100,103,104,106,111,110,112,115,116,118,121,122,124,128,128 %N A371638 a(n) = 2*n + valuation(n, 3) with valuation(n, 3) = A007949(n). %C A371638 See A371639 for the connection with Voronoi's congruence. %F A371638 a(n) = valuation(denominator(Voronoi(3, n))) where Voronoi(c, n) = ((c^n - 1) * bernoulli(n)) / (n * c^(n - 1)). %p A371638 A371638 := n -> 2*n + padic:-ordp(n, 3): seq(A371638(n), n = 1..64); %t A371638 Array[2 # + IntegerExponent[#, 3] &, 64] (* _Michael De Vlieger_, Mar 31 2024 *) %o A371638 (SageMath) %o A371638 def A371638(n): return 2 * n + valuation(n, 3) %o A371638 print([A371638(n) for n in range(1, 65)]) %Y A371638 Cf. A007949, A371639, A292608 (c=2). %K A371638 nonn,easy %O A371638 1,1 %A A371638 _Peter Luschny_, Mar 30 2024