|
| |
|
|
A211347
|
|
Numbers n such that n = sigma_k(m) for some k >= 1.
|
|
3
|
|
|
|
1, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 17, 18, 20, 21, 24, 26, 28, 30, 31, 32, 33, 36, 38, 39, 40, 42, 44, 48, 50, 54, 56, 57, 60, 62, 63, 65, 68, 72, 73, 74, 78, 80, 82, 84, 85, 90, 91, 93, 96, 98, 102, 104, 108, 110, 112, 114, 120, 121, 122
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
Sigma_k(n) = Sum[d|n, d^k].
Sigma_0(n) can be any positive integer and so is ignored in this sequence.
|
|
|
LINKS
|
Giovanni Resta, Table of n, a(n) for n = 1..10000
Eric W. Weisstein, MathWorld: Divisor function
|
|
|
EXAMPLE
|
Sigma_2(4) = 1 + 4 + 16 = 21 so 21 is in the sequence.
|
|
|
MATHEMATICA
|
upto[n_] := Select[Union@Flatten[{1, DivisorSigma[Range@Max[1, Floor@Log[#, n]], #] & /@ Range[2, n]}], # <= n &]; upto[122] (* Giovanni Resta, Feb 05 2013 *)
|
|
|
CROSSREFS
|
Cf. A000203, A001157, A001158, A001159, A001160.
Cf. A013954, A013955, A013956, A013957, A013958, A013959, A013960, A013961, A013962, A013963, A013964, A013965, A013966, A013967, A013968, A013969, A013970, A013971, A013972.
Cf. A000005.
Sequence in context: A304812 A026500 A091213 * A258777 A298004 A039238
Adjacent sequences: A211344 A211345 A211346 * A211348 A211349 A211350
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Jon Perry, Feb 05 2013
|
|
|
STATUS
|
approved
|
| |
|
|
