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Search: id:A120376
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| A120376 |
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Primes of the form 2*5^n-1. |
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+0
1
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| 1249, 31249, 305175781249, 119209289550781249, 1862645149230957031249, 111022302462515654042363166809082031249, 25243548967072377773175314089049159349542605923488736152648925781249
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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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, 1249 is 881 in base 12.
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FORMULA
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a(n) = n-th number such that 2*5^k-1 that is prime.
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EXAMPLE
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a(1)=4 since 2*5^4-1=1249 is the first prime.
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MAPLE
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for w to 1 do for k from 1 to 2000 do n:=2*5^k-1; if isprime(n) then printf("%d, %d", k, n) fi od od;
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CROSSREFS
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Cf. A000043, A000668, A002957, A002959, A003307, A079363, A055558.
Sequence in context: A047629 A020384 A086709 this_sequence A122272 A106322 A035762
Adjacent sequences: A120373 A120374 A120375 this_sequence A120377 A120378 A120379
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KEYWORD
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nonn
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AUTHOR
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Walter Kehowski (wkehowski(AT)cox.net), Jun 28 2006
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