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 A069810 #36 Sep 08 2022 08:45:05 %S A069810 1,56,60,96,132,184,204,248,276,348,376,480,492,504,564,568,612,632, %T A069810 636,708,824,852,996,1016,1068,1208,1212,1248,1284,1336,1356,1528, %U A069810 1572,1592,1632,1644,1784,1788,1908,1912,1980,2004,2076,2104,2148,2168,2232 %N A069810 Integers k such that gcd(k, sigma(k)) = tau(k). %H A069810 Giovanni Resta, <a href="/A069810/b069810.txt">Table of n, a(n) for n = 1..10000</a> %e A069810 The divisors of 56 are 1, 2, 4, 7, 8, 14, 28, 56, so tau(56) = 8 and sigma(56) = 120. As gcd(56, 120) = tau(56) = 8, so 56 belongs to this sequence. - _Bernard Schott_, Oct 18 2019 %t A069810 Select[Range[2500], GCD[DivisorSigma[1, #], #] == DivisorSigma[0, #] &] (* _Jayanta Basu_, Mar 21 2013 *) %o A069810 (PARI) for(n=1,3000,if(gcd(n, sigma(n))==numdiv(n),print1(n,","))) %o A069810 (Magma) [k:k in [1..2300]| Gcd(k,DivisorSigma(1,k)) eq #Divisors(k)]; // _Marius A. Burtea_, Oct 18 2019 %Y A069810 Subsequence of A047727 (numbers that are arithmetic and refactorable). %Y A069810 Cf. A003601 (arithmetic numbers), A033950 (refactorable numbers). %K A069810 easy,nonn %O A069810 1,2 %A A069810 _Benoit Cloitre_, Apr 30 2002