OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
EXAMPLE
72 = sigma(30) = sigma(46) = sigma(51) = sigma(55) = sigma(71).
MATHEMATICA
a = Table[ 0, {5000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 5001, a[ [ s ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 5000 ], a[ [ # ] ] == 5 & ]
With[{upto=5000}, Select[Union[Transpose[Select[Tally[DivisorSigma[ 1, Range[ upto]]], #[[2]]==5&]][[1]]], #<=upto&]] (* Harvey P. Dale, Jan 27 2015 *)
PROG
(PARI) is(k) = invsigmaNum(k) == 5 \\ Amiram Eldar, Nov 17 2024, using Max Alekseyev's invphi.gp
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Robert G. Wilson v, Apr 18 2001
STATUS
approved