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

1,3

Comments

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

Links

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

Example

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

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 *)

Crossrefs

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

Sequence in context: A224892 A351233 A265517 * A063973 A126441 A004181

Adjacent sequences: A063969 A063970 A063971 * A063973 A063974 A063975

Keyword

nonn

Author

Labos Elemer, Sep 05 2001

Extensions

Edited by Don Reble, May 14 2006

Status

approved