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

1,1

Links

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

Example

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.

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

Prog

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

Crossrefs

Cf. A000396, A066961, A081357.

Sequence in context: A047658 A290804 A353365 * A264873 A116058 A231692

Adjacent sequences: A146539 A146540 A146541 * A146543 A146544 A146545

Keyword

nonn

Author

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

Extensions

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

a(20) from Daniel Suteu, May 23 2022

Status

approved