A060660 Sigma(x) = n has exactly four solutions.

96, 120, 180, 312, 372, 420, 434, 456, 540, 546, 560, 624, 702, 728, 798, 816, 930, 1064, 1120, 1170, 1404, 1632, 1638, 1674, 1710, 1776, 1792, 1944, 2100, 2240, 2544, 2560, 2664, 2760, 2800, 2844, 2856, 2940, 2952, 3000, 3040, 3048, 3060, 3080, 3096

Offset

1,1

Links

Table of n, a(n) for n=1..45.

Example

96 = sigma(42) = sigma(62) = sigma(69) = sigma(77).

Mathematica

a = Table[ 0, {5000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 5001, a[ [ s ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 5000 ], a[ [ # ] ] == 4 & ]

Crossrefs

Cf. A007370, A007371, A007372.

Sequence in context: A257411 A175116 A153484 * A258748 A323629 A146992

Adjacent sequences: A060657 A060658 A060659 * A060661 A060662 A060663

Keyword

nonn

Author

Robert G. Wilson v, Apr 18 2001

Status

approved