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 A146542 #21 May 23 2022 03:57:44 %S A146542 5,12,427,10924032,16125952,22017387,24376323,32501857,33288097, %T A146542 3757637632,6241076643,8522760577,45091651584,66563866624,86692869921, %U A146542 137421905953,137437511683,727145809044307968,1152771972099211264,845044701535107443245558061611352064 %N A146542 Numbers m such that sigma(m) is a perfect number. %H A146542 Daniel Suteu, <a href="/A146542/b146542.txt">Table of n, a(n) for n = 1..58</a> %e A146542 The divisors of 5 are 1 and 5, which add up to 6. 6 is a perfect number because its proper divisors are 1, 2 and 3, which also add up to 6. %p A146542 with(numtheory); P:=proc(q) local n; for n from 1 to q do %p A146542 if sigma(sigma(n))=2*sigma(n) then print(n); %p A146542 fi; od; end: P(10^9); # _Paolo P. Lava_, Oct 22 2013 %o A146542 (PARI) isok(n) = sigma(sigma(n)) == 2*sigma(n); \\ _Michel Marcus_, Oct 22 2013 %Y A146542 Cf. A000396, A066961, A081357. %K A146542 nonn %O A146542 1,1 %A A146542 Howard Berman (howard_berman(AT)hotmail.com), Oct 31 2008 %E A146542 Two missing terms added and a(10)-a(19) from _Donovan Johnson_, Jan 20 2012 %E A146542 a(20) from _Daniel Suteu_, May 23 2022