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 A115557 #23 Jan 31 2025 04:21:15 %S A115557 1,49,121,169,361,529,841,961,1849,2209,2809,5329,6889,9409,10609, %T A115557 12769,16129,24649,32041,38809,39601,49729,51529,54289,57121,58081, %U A115557 63001,66049,73441,78961,96721,99856,100489,110889,124609,151321,160801 %N A115557 Squares in A076361. %C A115557 The commutator [sigma, tau] is zero, that is, A076360(x) = 0 and x is a square. %H A115557 Giovanni Resta, <a href="/A115557/b115557.txt">Table of n, a(n) for n = 1..10000</a> %F A115557 a(n) = A115558(n)^2. - _Amiram Eldar_, Jan 31 2025 %e A115557 The special squared prime 121 is a term because it is a square and sigma(tau(121)) = sigma(3) = 4 = tau(sigma(121)) = tau(1 + 11 + 121) = tau(133) = 4. %e A115557 The least solution with composite square root is 316^2 = 99856: tau(99856) = 15, sigma(15) = 24 or sigma(99856) = 195951 = 3*7*7*31*43, tau(195951) = 24. %t A115557 ds = DivisorSigma; Select[Range[1000]^2, ds[0, ds[1, #]] == ds[1, ds[0, #]] &] (* _Giovanni Resta_, Apr 29 2017 *) %o A115557 (PARI) isok(n) = issquare(n) && (sigma(numdiv(n)) == numdiv(sigma(n))); \\ _Michel Marcus_, Dec 20 2013 %Y A115557 Cf. A000005, A000203, A062068, A062069, A076360, A076361, A115558. %K A115557 nonn %O A115557 1,2 %A A115557 _Labos Elemer_, Jan 25 2006