A107036 Indices of prime Jacobsthal numbers.

3, 4, 5, 7, 11, 13, 17, 19, 23, 31, 43, 61, 79, 101, 127, 167, 191, 199, 313, 347, 701, 1709, 2617, 3539, 5807, 10501, 10691, 11279, 12391, 14479, 42737, 83339, 95369, 117239, 127031, 138937, 141079, 267017, 269987, 374321, 986191, 4031399

Offset: 1

Author

Paul Barry, May 09 2005

Keywords

• nonn
• more

Comments

All terms are prime except a(1) = 4. All prime terms are listed in A000978. - Alexander Adamchuk, Oct 03 2006

Crossrefs

Cf. A000978, A001045, A001605.

Programs

PARI

is(n)=ispseudoprime((2^n - (-1)^n) / 3) \\ Charles R Greathouse IV, Apr 28 2015

Formula

a(n) = A000978(n-1) for n >= 3. - Alexander Adamchuk, Oct 03 2006

Extensions

More terms from Alexander Adamchuk, Oct 03 2006

a(41)-a(42) from Bill McEachen, Aug 28 2024