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%I #12 Mar 15 2023 12:36:27
%S 241,428717761
%N Primes of the form 2*11^n-1.
%C 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.
%C The n<1000 that yield primes are 2, 8, 248. - _T. D. Noe_, Nov 16 2006
%F a(n) = n-th number such that 2*11^k-1 that is prime for some k.
%F a(n) = 2*11^A120378(n)-1. - _R. J. Mathar_, Mar 06 2010
%e a(1)=241 since 2*11^2-1=241 is the first prime.
%p 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;
%t Select[2*11^Range[1000]-1, PrimeQ] (* _T. D. Noe_, Nov 16 2006 *)
%Y Cf. A000043, A000668, A002957, A002959, A003307, A079363, A055558.
%K nonn,bref
%O 1,1
%A _Walter Kehowski_, Jun 28 2006
%E Corrected by _T. D. Noe_, Nov 16 2006
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