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%I #14 Jan 07 2017 00:52:17
%S 25,77,403,1121,3379,7697,16897,25769,56341,63983,107447,129709,
%T 192403,222529,238999,328157,361259,466933,515909,645719,817009,
%U 1219637,1299433,1508917,1952359,2359943,2642597,2815831,3060037,3260713
%N Product of twin-prime-indexed primes and their upper bound twin prime.
%F Let prime(i) = i-th prime, let twin(n) = (P, Q) be n-th pair of twin primes; sequence gives prime(P)*Q.
%e The 3rd pair of twin primes is twin(3) = (11,13), prime(11) = 31, a(3) = 31*13 = 403.
%o (PARI) twipxpindex2(n) = {sr=0; pr=1; for(x=1,n, p1=prime(x); p2=prime(x+1); if((p2-p1)==2, pr=p2*prime(prime(x)); sr+=1.0/pr; print1(pr" ")); ); print(); print(sr) }
%Y Cf. A057470.
%K easy,nonn
%O 1,1
%A _Cino Hilliard_, Mar 04 2003
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