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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 21 12:12 EDT 2019. Contains 328299 sequences. (Running on oeis4.)