A123176 - OEIS

A123176

Numbers n such that (2^p + 1)/3 is prime, where p is the n-th prime.

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

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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

Table of n, a(n) for n=1..41.

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

Cf. A000978, A000979, A001045, A049883, A107036, A123214.

Sequence in context: A082324 A219955 A079064 * A017902 A005710 A367800

Adjacent sequences: A123173 A123174 A123175 * A123177 A123178 A123179

KEYWORD

more,nonn

AUTHOR

Alexander Adamchuk, Oct 03 2006

EXTENSIONS

Two more terms computed from A000978 by Max Alekseyev, Mar 03 2010

STATUS

approved