A259174 Numbers whose abundance is a power of 2.

12, 20, 56, 70, 88, 104, 108, 220, 368, 464, 550, 572, 650, 748, 836, 860, 952, 992, 1232, 1504, 1672, 1888, 1952, 2140, 2392, 2744, 3708, 4030, 5336, 5830, 6328, 6536, 6808, 7192, 7304, 7544, 7912, 8968, 9656, 9820, 10184, 10792, 11096, 13496, 14008

Offset

1,1

Comments

Subsequence of A005101 whose abundance is a term of A000079 except 1.

Below 35*10^8, only 236925 is odd and its abundance is 2^9.

Least term whose abundance has an exponent, e, of two for e>0: 20, 12, 56, 550, 572, 108, 860, 952, 1232, 6328, 3708, 40540, 37072, 79288, 327260, 357112, 302000, 527296, 1764056, 6506512, 38559776, 21893248, 42257216, 167771740, 90798560, 469761208, 508198064, 490304800, 1353048560, 2951488480, ..., .

Links

Robert G. Wilson v, Table of n, a(n) for n = 1..482

Mathematica

fQ[n_] := IntegerQ@ Log2[DivisorSigma[1, n] - 2 n]; Select[ Range@ 15000, fQ]

Prog

(PARI) isok(n) = isprimepower(sigma(n)-2*n, &p) && (p==2); \\ Michel Marcus, Mar 25 2017

Crossrefs

Cf. A005101.

Sequence in context: A282754 A063690 A229355 * A109788 A341361 A181701

Adjacent sequences: A259171 A259172 A259173 * A259175 A259176 A259177

Keyword

nonn

Author

Robert G. Wilson v, Jun 20 2015

Status

approved