A060661 Sigma(x) = n has exactly five solutions.

72, 144, 192, 216, 588, 600, 648, 792, 936, 992, 1056, 1224, 1302, 1320, 1560, 1736, 1980, 2040, 2088, 2112, 2268, 2448, 2730, 2790, 2912, 3038, 3136, 3312, 3472, 3520, 3534, 3552, 3672, 3792, 3816, 3936, 4056, 4092, 4340, 4440, 4864, 4872, 4920, 4960

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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 *)

Crossrefs

Cf. A007370, A007371, A007372.

Sequence in context: A157336 A369333 A369334 * A050495 A137883 A173728

Adjacent sequences: A060658 A060659 A060660 * A060662 A060663 A060664

Keyword

nonn

Author

Robert G. Wilson v, Apr 18 2001

Status

approved