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 A146542 Numbers m such that sigma(m) is a perfect number. 2
 5, 12, 427, 10924032, 16125952, 22017387, 24376323, 32501857, 33288097, 3757637632, 6241076643, 8522760577, 45091651584, 66563866624, 86692869921, 137421905953, 137437511683, 727145809044307968, 1152771972099211264, 845044701535107443245558061611352064 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 15 08:18 EDT 2024. Contains 375173 sequences. (Running on oeis4.)