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 A115558 #14 Jan 28 2025 01:46:13 %S A115558 1,7,11,13,19,23,29,31,43,47,53,73,83,97,103,113,127,157,179,197,199, %T A115558 223,227,233,239,241,251,257,271,281,311,316,317,333,353,389,401,409, %U A115558 419,421,443,449,461,467,479,491,503,509,549,563,587,593,599,617,641 %N A115558 a(n) is the square root of A115557(n). %H A115558 Giovanni Resta, <a href="/A115558/b115558.txt">Table of n, a(n) for n = 1..10000</a> %F A115558 The commutator [sigma, tau] is zero and a(n) is the square root of solutions. Both prime and composite numbers. %t A115558 Select[Range[1000], DivisorSigma[0, DivisorSigma[1, #^2]] == DivisorSigma[1, DivisorSigma[0, #^2]] &] (* _Amiram Eldar_, Jan 28 2025 *) %o A115558 (PARI) isok(k) = numdiv(sigma(k^2)) == sigma(numdiv(k^2)); \\ _Amiram Eldar_, Jan 28 2025 %Y A115558 Cf. A000005, A000203, A076360, A076361, A062068, A062069, A115557, A115559, A115560. %K A115558 nonn %O A115558 1,2 %A A115558 _Labos Elemer_, Jan 25 2006