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%I #4 Mar 30 2012 18:36:04
%S 3,9,15,45,225,639,1275,4005,675405,2203959,3075159,6195234165,
%T 77989711185,4566262987329
%N a(1)=3; a(n)=first odd number greater than a(n-1) such that 2*a(n)-1 is prime and a(i)+a(n)-1 is prime for all 1<=i<=n-1.
%C All elements are 3 mod 6. In base 12 the sequence is 3, 9, 13, 39, 169, 453, 8X3, 2399, 286X39, 8X3533, 1043733, where X is 10 and E is eleven.
%F a(1)=3; a(n) = s where s is the first odd number s>a(n-1) such that 2*s-1 is prime and s+a(i)-1 is prime, 1<=i<=n-1.
%F a(n) = A119752(n) + 1. - Chandler
%e a(2)=9 since 9 is the first odd number > a(1)=3 such that 2*9-1=17 is prime and 9+3-1=13 is prime.
%p OP:=[3]: for w to 1 do for k from 0 to 12^8 do n:=6*k+3; p:=2*n-1; Q:=map(z-> z+n-1, OP); if isprime(p) and andmap(isprime,Q) then OP:=[op(OP), n]; print(n); fi od od;
%Y Cf. A119752, A119754 (resulting primes), A119751, A119753, A103828.
%K nonn,more
%O 1,1
%A _Walter Kehowski_, Jul 02 2006
%E a(12)-a(14) from _Ray Chandler_, Apr 04 2010
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