%I #21 May 23 2022 03:57:44

%S 5,12,427,10924032,16125952,22017387,24376323,32501857,33288097,

%T 3757637632,6241076643,8522760577,45091651584,66563866624,86692869921,

%U 137421905953,137437511683,727145809044307968,1152771972099211264,845044701535107443245558061611352064

%N Numbers m such that sigma(m) is a perfect number.

%H Daniel Suteu, <a href="/A146542/b146542.txt">Table of n, a(n) for n = 1..58</a>

%e 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 with(numtheory); P:=proc(q) local n; for n from 1 to q do

%p if sigma(sigma(n))=2*sigma(n) then print(n);

%p fi; od; end: P(10^9); # _Paolo P. Lava_, Oct 22 2013

%o (PARI) isok(n) = sigma(sigma(n)) == 2*sigma(n); \\ _Michel Marcus_, Oct 22 2013

%Y Cf. A000396, A066961, A081357.

%K nonn

%O 1,1

%A Howard Berman (howard_berman(AT)hotmail.com), Oct 31 2008

%E Two missing terms added and a(10)-a(19) from _Donovan Johnson_, Jan 20 2012

%E a(20) from _Daniel Suteu_, May 23 2022