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A231755 Primes of the form (2^n-1)/3 - n. 1
331, 1398079, 89478457, 393530540239137101071, 1730765619511609209510165443073253, 8173309551284740577911184144801648979299941984979211421, 2142584059011987034055949456454883470029603991710390447068299 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(14) has 671 digits. a(15) has 2820 digits (not included in b-file).

Alternately, primes of the form Jacobsthal(n) - n, where Jacobsthal(n) is the n-th Jacobsthal number.

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..14

EXAMPLE

a(2)= 1398079: n=22: ((2^n-(-1)^n)/3-n)= 1398079, which is prime.

a(4)= 393530540239137101071: n=70: ((2^n-(-1)^n)/3-n)= 393530540239137101071, which is prime.

MAPLE

KD := proc() local a; a:= (2^n -(-1)^n)/3-n; if isprime(a)then RETURN (a); fi; end: seq(KD(), n=1..1000);

PROG

(PARI) for(n=8, 500, if(ispseudoprime(t=2^n\/3-n), print1(t", "))) \\ Charles R Greathouse IV, Nov 13 2013

CROSSREFS

Cf. A001045 (Jacobsthal numbers).

Cf. A107036 (indices of prime Jacobsthal numbers).

Cf. A128209 (Jacobsthal numbers+1).

Sequence in context: A199820 A255389 A133141 * A097401 A250758 A114084

Adjacent sequences:  A231752 A231753 A231754 * A231756 A231757 A231758

KEYWORD

nonn,less

AUTHOR

K. D. Bajpai, Nov 13 2013

EXTENSIONS

Definition corrected by Charles R Greathouse IV, Nov 13 2013

STATUS

approved

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Last modified April 16 18:53 EDT 2021. Contains 343050 sequences. (Running on oeis4.)