A060664 Sigma(x) = n has exactly eight solutions.

336, 432, 672, 756, 840, 1536, 1620, 1764, 1848, 2280, 2394, 2604, 2808, 3264, 4080, 4480, 4860, 5328, 6528, 6624, 7128, 8316, 8568, 8880, 10608, 11040, 11448, 12288, 12420, 12636, 13176, 13200, 13248, 13536, 13860, 14196, 14208, 14448, 14700

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

336 = sigma(132) = sigma(140) = sigma(182) = sigma(188) = sigma(195) = sigma(249) = sigma(287) = sigma(299).

Maple

N:= 30000: # to get terms <= N
V:= Vector(N):
for k from 1 to N-1 do
  t:= numtheory:-sigma(k);
  if t <= N then V[t]:= V[t]+1 fi
od:
select(t -> V[t]=8, [$1..N]); # Robert Israel, Sep 22 2019

Mathematica

a = Table[ 0, {20000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 20001, a[ [ s ] ]++ ], {n, 1, 20000} ]; Select[ Range[ 20000 ], a[ [ # ] ] == 8 & ]

Crossrefs

Cf. A007370, A007371, A007372.

Sequence in context: A137522 A090487 A289220 * A261551 A247530 A064259

Adjacent sequences: A060661 A060662 A060663 * A060665 A060666 A060667

Keyword

nonn

Author

Robert G. Wilson v, Apr 18 2001

Status

approved