A209048 Indices of the pentagonal numbers listed in A209049.

1, 2, 4, 3, 12, 11, 32, 27, 75, 192, 427, 171, 1323, 2187, 6912, 8192, 4779, 10923, 49152, 109227, 60075, 170667, 786432, 699051, 1092267, 4893355, 5810859, 11184811, 25864875, 95070891, 101362347, 44739243

Offset: 0

Author

Robert G. Wilson v, Mar 04 2012

Keywords

• nonn

Comments

Pentagonal analog of A076550.

Crossrefs

A209049, A076550.

Programs

Mathematica

k = 1; t = Table[0, {50}]; While[k < 500000001, a = PrimeOmega[k] + PrimeOmega[3 k - 1] - 1; If[ t[[a + 1]] == 0, t[[a + 1]] = k; Print[{k, a}]]; k++]; t