A332739 Numbers k such that usigma(x) = k has a unique solution, where usigma(k) is the sum of unitary divisors of k (A034448).

1, 3, 4, 5, 6, 8, 9, 10, 14, 17, 26, 28, 33, 38, 40, 44, 56, 62, 65, 70, 74, 78, 82, 98, 100, 110, 112, 122, 129, 130, 136, 138, 158, 164, 174, 176, 182, 186, 190, 194, 208, 210, 212, 220, 222, 230, 238, 242, 244, 246, 248, 250, 256, 257, 258, 278, 282, 284, 290

Offset

1,2

Links

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

Mathematica

usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); m = 300; v = Table[ 0, {m}]; Do[u = usigma[k]; If[u <= m, v[[u]]++], {k, 1, m}]; Position[v, _?(# == 1 &)]//Flatten

Crossrefs

Cf. A007370, A034448, A064000.

Sequence in context: A063977 A290136 A359168 * A306588 A353300 A219636

Adjacent sequences: A332736 A332737 A332738 * A332740 A332741 A332742

Keyword

nonn

Author

Amiram Eldar, Feb 21 2020

Status

approved