A291453 Numbers n such that A291356(n) > 0.

0, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 16, 17, 18, 21, 24, 25, 26, 28, 31, 32, 34, 36, 38, 44, 50, 51, 61, 66, 68, 73, 79, 83, 86, 87, 95, 132, 138, 139, 144, 159, 162, 167, 177, 183, 188, 189, 191, 194, 213, 230, 242, 253, 255, 265, 273, 274, 277, 287, 300, 310, 311, 337, 338, 352

Offset: 1

Author

Amiram Eldar and Altug Alkan, Aug 24 2017

Keywords

• nonn

Comments

Searching until n = 2500, we have found only 11 values of n with more than one solution to usigma(x) = prime(n)#: 8, 11, 13, 17, 24, 38, 86 have 2 solutions and 3, 5, 6, 7 have 3 solutions. Are these the only numbers with more than one solution?

Examples

			For n = 6 there are 3 solutions: usigma(20018) = usigma(29504) = usigma(30029) = 30030 = A002110(6).
		

Crossrefs

Cf. A291356.

Programs

Mathematica

primorial[n_] := Product[Prime[i], {i, n}]; a[k_] := Module[{n = primorial[k], m = 1}, s = {};
If[PrimePowerQ[n - 1], AppendTo[s, n - 1]];
While[2^m0 &)]]