A007621 Impractical numbers: even abundant numbers (A173490) that are not practical(2) (A007620). (Formerly M5337)

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

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

Robert G. Wilson v, Letter to N. J. A. Sloane, date unknown.

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 * A353061 A051971 A180274

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