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 A120377 Primes of the form 2*11^n-1. 1
 241, 428717761 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. The n<1000 that yield primes are 2, 8, 248. - T. D. Noe, Nov 16 2006 LINKS FORMULA a(n) = n-th number such that 2*11^k-1 that is prime for some k. a(n) = 2*11^A120378(n)-1. [From R. J. Mathar, Mar 06 2010] EXAMPLE a(1)=241 since 2*11^2-1=241 is the first prime. MAPLE 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; MATHEMATICA Select[2*11^Range[1000]-1, PrimeQ] - T. D. Noe, Nov 16 2006 CROSSREFS Cf. A000043, A000668, A002957, A002959, A003307, A079363, A055558. Sequence in context: A207286 A217998 A183891 * A171242 A060110 A113468 Adjacent sequences:  A120374 A120375 A120376 * A120378 A120379 A120380 KEYWORD nonn,bref AUTHOR Walter Kehowski, Jun 28 2006 EXTENSIONS Corrected by T. D. Noe, Nov 16 2006 STATUS approved

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