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 A071834 #27 Jan 15 2018 08:53:33 %S A071834 6,28,40,84,117,120,135,140,224,234,270,420,468,496,585,672,756,775, %T A071834 819,891,931,936,1080,1120,1170,1287,1372,1488,1550,1625,1638,1782, %U A071834 1862,2176,2299,2325,2340,2480,2574,2793,3100,3159,3250,3276,3360,3472 %N A071834 Numbers n > 1 such that n and sigma(n) have the same largest prime factor. %C A071834 By pure convention, we could include a leading 1 to this sequence, as someone using the mathematically arguably value A006530(1) = 1 might search for this sequence with a leading 1. However, this was not done in view of the age of this sequence. - _Rémy Sigrist_, Jan 09 2018 %H A071834 Michel Marcus, <a href="/A071834/b071834.txt">Table of n, a(n) for n = 1..1000</a> %F A071834 n such that A006530(n) = A006530(sigma(n)). %F A071834 n such that A006530(n) = A071190(n). - _Michel Marcus_, Oct 11 2017 %e A071834 1550 = 2*5^2*31 and sigma(1550) = 2976 = 2^5*3*31 hence 1550 is in the sequence. %t A071834 fQ[n_] := FactorInteger[n][[-1, 1]] == FactorInteger[DivisorSigma[1, n]][[-1, 1]]; Rest@ Select[ Range@3500, fQ] (* _Robert G. Wilson v_, Jan 09 2018 *) %o A071834 (PARI) for(n=2,1000,if(component(component(factor(n),1),omega(n)) == component(component(factor(sigma(n)),1),omega(sigma(n))), print1(n,","))) %o A071834 (PARI) isok(n) = vecmax(factor(n)[,1]) == vecmax(factor(sigma(n))[,1]); \\ _Michel Marcus_, Sep 29 2017 %Y A071834 Cf. A000203 (sigma), A006530 (gpf), A071190. %Y A071834 A000396 (perfect numbers) is a subsequence. %K A071834 easy,nonn %O A071834 1,1 %A A071834 _Benoit Cloitre_, Jun 08 2002