A080698 Product of twin-prime-indexed primes and their lower bound twin prime.
15, 55, 341, 1003, 3161, 7339, 16343, 25063, 55247, 62809, 105901, 127991, 190277, 220223, 236597, 325291, 358261, 463487, 512263, 641593, 812327, 1213843, 1293431, 1502399, 1944893, 2351677, 2633803, 2806733, 3050519, 3250847
Offset: 1
Examples
The 3rd pair of twin primes is twin(3) = (11,13), prime(11) = 31. a(3) = 31*11 = 341.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Crossrefs
Cf. A057470.
Programs
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Mathematica
# Prime[#]&/@Select[Partition[Prime[Range[200]],2,1],#[[2]]-#[[1]]==2&][[All,1]] (* Harvey P. Dale, Apr 10 2019 *)
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PARI
twipxpindex(n) = {sr=0; pr=1; for(x=1,n, p1=prime(x); p2=prime(x+1); if((p2-p1)==2, pr=p1*prime(prime(x)); sr+=1.0/pr; print1(pr" ")); ); print(); print(sr) }
Formula
Let prime(i) = i-th prime, let twin(n) = (P, Q) be n-th pair of twin primes; sequence gives prime(P)*P.