A205881 Second pentagonal numbers that are interprime.

15, 26, 260, 495, 610, 950, 1190, 1962, 2420, 2667, 3197, 3337, 3480, 6370, 7597, 14455, 15965, 18205, 39447, 42926, 43947, 50325, 57135, 63140, 64377, 65000, 66255, 74037, 78090, 82251, 86520, 87967, 106267, 107870, 121980, 125426, 136957, 140607, 153760

Offset: 1

Author

Zak Seidov, Feb 01 2012

Keywords

• nonn

Comments

Intersection of A005449 and A024675. Also see references in A075190 about interprimes of different forms.

Examples

			a(1) = 15 = A024675(5) = A005449(3).
a(2) = 26 = A024675(8) = A005449(4).
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A005449, A024675, A075190.

Programs

Mathematica

Select[Mean/@Partition[Prime[Range[15000]],2,1],IntegerQ[(Sqrt[1+24#]-1)/6]&] (* Harvey P. Dale, Feb 02 2020 *)