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A120377
Primes of the form 2*11^n-1.
3
241, 428717761
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
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. - 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 *)
KEYWORD
nonn,bref
AUTHOR
Walter Kehowski, Jun 28 2006
EXTENSIONS
Corrected by T. D. Noe, Nov 16 2006
STATUS
approved