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A120378
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Integers n such that 2*11^n-1 is prime.
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6
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OFFSET
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1,1
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COMMENTS
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See comments for A057472. Examined in base 12, all n must be even and all primes must be 1-primes. For example, 241 is 181 in base 12.
a(9) > 2*10^5. - Robert Price, Nov 06 2015
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LINKS
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Table of n, a(n) for n=1..8.
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FORMULA
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a(n) = n-th integer k such that 2*11^k-1 is prime.
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EXAMPLE
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a(1)=2 since 2*11^2-1=241 is the first prime of this form.
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MAPLE
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for w to 1 do for k from 1 to 2000 do n:=2*11^k-1; if isprime(n) then printf("%d, %d", k, n) fi od od;
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MATHEMATICA
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Select[Range[0, 200000], PrimeQ[2*11^# - 1] &] (* Robert Price, Nov 06 2015 *)
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CROSSREFS
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Cf. A000043, A000668, A002957, A002959, A003307, A079363, A055558.
Sequence in context: A125264 A028985 A067583 * A012345 A012341 A299374
Adjacent sequences: A120375 A120376 A120377 * A120379 A120380 A120381
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KEYWORD
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more,nonn
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AUTHOR
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Walter Kehowski, Jun 28 2006
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EXTENSIONS
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More terms from Ryan Propper, Jan 14 2008
a(7)-a(8) from Robert Price, Nov 06 2015
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STATUS
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approved
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