|
| |
|
|
A007621
|
|
Impractical numbers: even abundant numbers (A173490) that are not practical(2) (A007620).
(Formerly M5337)
|
|
2
|
|
|
|
70, 102, 114, 138, 174, 186, 222, 246, 258, 282, 318, 350, 354, 366, 372, 402, 426, 438, 444, 474, 490, 492, 498, 516, 534, 550, 564, 572, 582, 606, 618, 636, 642, 650, 654, 678, 708, 732, 738, 748, 762, 770, 774, 786, 804, 822, 834, 836, 846, 852, 876, 894
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
REFERENCES
|
R. Honsberger, Mathematical Gems, M.A.A., 1973, p. 113.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
|
|
|
LINKS
|
T. D. Noe, Table of n, a(n) for n = 1..1000
|
|
|
MATHEMATICA
|
practicalQ[n_] := Module[{d = Divisors[n], c}, c = Rest[CoefficientList[Series[Product[1 + x^d[[i]], {i, Length[d]}], {x, 0, n}], x]]; Flatten[Position[c, 0]] == {} && c[[-1]] > 1]; Select[2*Range[500], DivisorSigma[1, #] > 2 # && ! practicalQ[#] &] (* T. D. Noe, Jun 25 2012 *)
|
|
|
CROSSREFS
|
A173490 with A007620 removed. Cf. A035480.
Sequence in context: A136117 A224553 A156718 * A051971 A180274 A075004
Adjacent sequences: A007618 A007619 A007620 * A007622 A007623 A007624
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
N. J. A. Sloane, Mira Bernstein, Robert G. Wilson v
|
|
|
EXTENSIONS
|
More terms from David W. Wilson.
|
|
|
STATUS
|
approved
|
| |
|
|
