A146542 Numbers m such that sigma(m) is a perfect number.

5, 12, 427, 10924032, 16125952, 22017387, 24376323, 32501857, 33288097, 3757637632, 6241076643, 8522760577, 45091651584, 66563866624, 86692869921, 137421905953, 137437511683, 727145809044307968, 1152771972099211264, 845044701535107443245558061611352064

Offset: 1

Author

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

Keywords

• nonn

Examples

			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.
		

Links

• Daniel Suteu, Table of n, a(n) for n = 1..58

Crossrefs

Cf. A000396, A066961, A081357.

Programs

Maple

with(numtheory); P:=proc(q) local n; for n from 1  to q do
if sigma(sigma(n))=2*sigma(n) then print(n);
fi; od; end: P(10^9); # Paolo P. Lava, Oct 22 2013

PARI

isok(n) = sigma(sigma(n)) == 2*sigma(n); \\ Michel Marcus, Oct 22 2013

Extensions

Two missing terms added and a(10)-a(19) from Donovan Johnson, Jan 20 2012

a(20) from Daniel Suteu, May 23 2022