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Numbers k such that (2^(2k + 1) - 2)/3 + k - 1 is prime.
3

%I #19 Jul 30 2024 07:30:06

%S 1,2,4,10,14,28,54,62,124,592,1088,3154,3920,5564,26510,28674,65124

%N Numbers k such that (2^(2k + 1) - 2)/3 + k - 1 is prime.

%C These primes are represented in the numeral system described in A235860 with the digit "2" followed to the right with k-1 "12" strings.

%e For n = 2, (2^5 - 2)/3 + 1 = 11, which is prime, so 2 is in the sequence.

%o (PARI) isok(n) = isprime((2^(2*n+1) -2)/3 + n-1); \\ _Michel Marcus_, Jan 28 2014

%Y Cf. A235860.

%K nonn

%O 1,2

%A _Robin Garcia_, Jan 28 2014

%E a(1) inserted and a(15)-a(17) from _Michael S. Branicky_, Jul 29 2024