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 A001876 #38 Nov 25 2023 04:34:26
%S A001876 0,1,1,1,1,1,2,1,1,1,1,2,2,1,1,1,2,1,2,1,1,2,2,1,2,1,2,1,1,1,2,2,2,2,
%T A001876 1,1,3,1,1,1,1,2,3,1,2,1,2,1,3,1,1,2,2,1,2,2,2,1,1,1,2,2,2,2,2,1,4,1,
%U A001876 1,1,1,2,3,1,1,1,2,2,3,1,2,2,2,1,3,1,2,1
%N A001876 Number of divisors of n of the form 5k+1; a(0)=0.
%H A001876 T. D. Noe, <a href="/A001876/b001876.txt">Table of n, a(n) for n = 0..10000</a>
%H A001876 R. A. Smith and M. V. Subbarao, <a href="https://doi.org/10.4153/CMB-1981-005-3">The average number of divisors in an arithmetic progression</a>, Canadian Mathematical Bulletin, Vol. 24, No. 1 (1981), pp. 37-41.
%F A001876 G.f.: Sum_{n>=0} x^(5n+1)/(1-x^(5n+1)).
%F A001876 G.f.: Sum_{n>=1} x^n/(1-x^(5*n)). - _Joerg Arndt_, Jan 30 2011
%F A001876 Sum_{k=1..n} a(k) = n*log(n)/5 + c*n + O(n^(1/3)*log(n)), where c = gamma(1,5) - (1 - gamma)/5 = A256779 - (1 - A001620)/5 = 0.651363... (Smith and Subbarao, 1981). - _Amiram Eldar_, Nov 25 2023
%t A001876 CoefficientList[ Series[ Together[ Sum[ x^n/(1 - x^(5n)), {n, 110}]], {x, 0, 110}], x] (* _Robert G. Wilson v_, Jan 31 2011 *)
%t A001876 a[n_] := DivisorSum[n, 1 &, Mod[#, 5] == 1 &]; a[0] = 0; Array[a, 100, 0] (* _Amiram Eldar_, Nov 25 2023 *)
%o A001876 (PARI) a(n) = if(n==0,0, sumdiv(n, d, (d % 5) == 1)); \\ _Michel Marcus_, Feb 25 2021
%Y A001876 For numbers of divisors of n of the form 5k+i (i=1, 2, 3, 4) see: this sequence, A001877, A001878, A001899.
%Y A001876 Cf. A001620, A256779.
%K A001876 nonn,easy
%O A001876 0,7
%A A001876 _N. J. A. Sloane_