A063972 a(n) is the smallest m such that usigma(m) = n (or 0 if no such m).

1, 0, 2, 3, 4, 5, 0, 7, 8, 9, 0, 6, 0, 13, 0, 0, 16, 10, 0, 12, 0, 0, 0, 14, 0, 25, 0, 27, 0, 18, 0, 21, 32, 0, 0, 22, 0, 37, 0, 28, 0, 26, 0, 43, 0, 0, 0, 33, 0, 36, 0, 0, 0, 34, 0, 39, 0, 0, 0, 38, 0, 61, 0, 0, 64, 0, 0, 48, 0, 52, 0, 30, 0, 73, 0, 0, 0, 50, 0, 57, 0, 81, 0, 54, 0, 0, 0, 0, 0

Offset: 1

Author

Labos Elemer, Sep 05 2001

Keywords

• nonn

Comments

usigma(m) is the sum of unitary divisors of m, A034448.

Examples

			a(12)=6 because the unitary divisors of 6 are 1,2,3,6; they sum to 12.
		

Links

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

Crossrefs

Cf. A034444, A034448, A051444, A057637, A063973.

Programs

Mathematica

usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); m = 100; v = Table[0, {m}];  Do[u = usigma[n]; If[u <= m && v[[u]] == 0, v[[u]] = n], {n, 1, m}]; v (* Amiram Eldar, Sep 22 2019 *)

Extensions

Edited by Don Reble, May 14 2006