

A146542


Numbers n such that sigma(n) is a perfect number.


0



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

1,1


COMMENTS

727145809044307968 and 1152771972099211264 are also terms.  Donovan Johnson, Jan 20 2012


LINKS

Table of n, a(n) for n=1..17.


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. A066961, A081357.
Sequence in context: A195538 A047658 A290804 * 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(17) from Donovan Johnson, Jan 20 2012


STATUS

approved



