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 A072910 #16 Jun 06 2020 10:45:17 %S A072910 1,3,6,6,7,8,9,10,9,12,12,15,14,12,14,13,18,19,18,15,18,15,20,14,24, %T A072910 21,18,21,24,18,24,21,27,33,30,28,28,32,36,30,21,26,27,24,27,38,30,36, %U A072910 35,45,36,42,39,26,44,28,40,51,30,36,28,48,54,42,45,38,31,39,36,48,60,54 %N A072910 a(n) = sigma(A023883(n)) / tau(A023883(n)). %C A072910 Arithmetic means of divisors of nonprime arithmetic numbers (A023883). - _Amiram Eldar_, Jun 06 2020 %H A072910 Amiram Eldar, <a href="/A072910/b072910.txt">Table of n, a(n) for n = 1..10000</a> %t A072910 meanDiv[n_] := DivisorSigma[1, n]/DivisorSigma[0, n]; Select[meanDiv /@ Select[Range[200], !PrimeQ[#] &], IntegerQ] (* _Amiram Eldar_, Jun 06 2020 *) %o A072910 (PARI) f(x) = sigma(x)/numdiv(x); %o A072910 apply(x->f(x), select(x->((denominator(f(x))==1) && !isprime(x)), [1..1000])) \\ _Michel Marcus_, Jun 06 2020 %Y A072910 Cf. A000005, A000203, A003601, A102187, A023883. %K A072910 easy,nonn %O A072910 1,2 %A A072910 _Benoit Cloitre_, Aug 10 2002