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Second pentagonal numbers that are interprime.
1

%I #14 Feb 02 2020 14:04:41

%S 15,26,260,495,610,950,1190,1962,2420,2667,3197,3337,3480,6370,7597,

%T 14455,15965,18205,39447,42926,43947,50325,57135,63140,64377,65000,

%U 66255,74037,78090,82251,86520,87967,106267,107870,121980,125426,136957,140607,153760

%N Second pentagonal numbers that are interprime.

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

%H Zak Seidov, <a href="/A205881/b205881.txt">Table of n, a(n) for n = 1..1000</a>

%e a(1) = 15 = A024675(5) = A005449(3).

%e a(2) = 26 = A024675(8) = A005449(4).

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

%Y Cf. A005449, A024675, A075190.

%K nonn

%O 1,1

%A _Zak Seidov_, Feb 01 2012