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A123176
Numbers n such that (2^p + 1)/3 is prime, where p is the n-th prime.
2
2, 3, 4, 5, 6, 7, 8, 9, 11, 14, 18, 22, 26, 31, 39, 43, 46, 65, 69, 126, 267, 380, 495, 762, 1285, 1304, 1364, 1479, 1697, 4469, 8135, 9193, 11065, 11902, 12923, 13103, 23396, 23642, 31850, 77509, 285228
OFFSET
1,1
COMMENTS
Also prime(a(n)) are the indices of prime Jacobsthal numbers (A001045) with prime indices. Primes in the Jacobsthal sequence are listed in A049883.
LINKS
C. Caldwell's The Top Twenty, Wagstaff.
FORMULA
a(n) = A000720( A000978(n) ).
MATHEMATICA
Select[Range[500], PrimeQ[(2^Prime[#]+1)/3]&] (* The program generates the first 23 terms of the sequence. To generate more, increase the Range constant. *) (* Harvey P. Dale, Mar 09 2022 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Alexander Adamchuk, Oct 03 2006
EXTENSIONS
Two more terms computed from A000978 by Max Alekseyev, Mar 03 2010
STATUS
approved