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A080698
Product of twin-prime-indexed primes and their lower bound twin prime.
1
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
1,1
LINKS
FORMULA
Let prime(i) = i-th prime, let twin(n) = (P, Q) be n-th pair of twin primes; sequence gives prime(P)*P.
EXAMPLE
The 3rd pair of twin primes is twin(3) = (11,13), prime(11) = 31. a(3) = 31*11 = 341.
MATHEMATICA
# Prime[#]&/@Select[Partition[Prime[Range[200]], 2, 1], #[[2]]-#[[1]]==2&][[All, 1]] (* Harvey P. Dale, Apr 10 2019 *)
PROG
(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) }
CROSSREFS
Cf. A057470.
Sequence in context: A119658 A072745 A141839 * A082235 A219592 A104724
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Mar 04 2003
STATUS
approved