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 A366442 #14 Oct 10 2023 13:19:49
%S A366442 1,6,8,12,14,18,20,24,31,30,32,48,38,42,44,48,57,54,72,60,62,84,68,72,
%T A366442 74,96,80,84,108,90,112,120,98,102,104,108,110,114,144,144,133,156,
%U A366442 128,132,160,138,140,168,180,150,152,192,158,192,164,168,183,174,248
%N A366442 The sum of divisors of the 5-rough numbers (A007310).
%H A366442 Amiram Eldar, <a href="/A366442/b366442.txt">Table of n, a(n) for n = 1..10000</a>
%F A366442 a(n) = A000203(A007310(n)).
%F A366442 Sum_{k=1..n} a(k) ~ c * n^2, where c = zeta(2) = 1.644934... (A013661).
%F A366442 The asymptotic mean of the abundancy index of the 5-rough numbers: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k)/A007310(k) = Pi^2/9 = 1.0966227... (A100044).
%F A366442 In general, the asymptotic mean of the abundancy index of the prime(k)-rough numbers is zeta(2) * Product_{i=1..k-1} (1 - 1/prime(i)^2).
%t A366442 a[n_] := DivisorSigma[1, 2*Floor[3*n/2] - 1]; Array[a, 100]
%o A366442 (PARI) a(n) = sigma((3*n)\2 << 1 - 1)
%o A366442 (Python)
%o A366442 from sympy import divisor_sigma
%o A366442 def A366442(n): return divisor_sigma((n+(n>>1)<<1)-1) # _Chai Wah Wu_, Oct 10 2023
%Y A366442 Cf. A000203, A013661, A007310, A100044, A366441.
%Y A366442 Similar sequences: A008438, A062822, A065764, A180114, A362986, A366439, A366440.
%K A366442 nonn,easy
%O A366442 1,2
%A A366442 _Amiram Eldar_, Oct 10 2023