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A231755
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Primes of the form (2^n-1)/3 - n.
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1
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331, 1398079, 89478457, 393530540239137101071, 1730765619511609209510165443073253, 8173309551284740577911184144801648979299941984979211421, 2142584059011987034055949456454883470029603991710390447068299
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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EXAMPLE
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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.
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MAPLE
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KD := proc() local a; a:= (2^n -(-1)^n)/3-n; if isprime(a)then RETURN (a); fi; end: seq(KD(), n=1..1000);
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PROG
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CROSSREFS
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Cf. A107036 (indices of prime Jacobsthal numbers).
Cf. A128209 (Jacobsthal numbers+1).
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KEYWORD
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nonn,less
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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