A180734 Numbers the absolute value of whose deficiency is a deficient number.

1, 2, 3, 4, 5, 8, 9, 10, 11, 12, 14, 16, 17, 18, 20, 21, 22, 23, 25, 26, 27, 32, 34, 35, 36, 38, 39, 40, 44, 47, 49, 50, 53, 55, 56, 57, 58, 59, 63, 64, 65, 68, 70, 72, 74, 75, 77, 80, 81, 82, 83, 85, 88, 92, 93, 94, 98, 100, 104, 106, 107, 108, 110, 115, 116, 117, 119, 121, 122, 125, 128

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

{n such that |A033879(n)| is in A005100}.

Example

a(1) = 1 because the deficiency of 1 is 1, and 1 is itself a deficient number.
a(10) = 12 because the deficiency of 12 is -4 and |-4| = 4 is a deficient number.
7 is not in the sequence because the deficiency of 7 is 6, and 6 is a perfect number.
13 is not in the sequence because the deficiency of 13 is 12, and 12 is an abundant number.

Mathematica

Deficiency[n_] := 2 n - DivisorSigma[1, n]; Select[Range[150], Deficiency[Abs[Deficiency[#]]] > 0 &]

Crossrefs

Cf. A000203, A000396, A005100, A005101, A005843, A033630, A033879.

Sequence in context: A037471 A080401 A288666 * A031482 A047369 A004827

Adjacent sequences: A180731 A180732 A180733 * A180735 A180736 A180737

Keyword

nonn,easy

Author

Jonathan Vos Post, Jan 21 2011

Status

approved