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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Adjacent sequences:  A080695 A080696 A080697 * A080699 A080700 A080701

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Mar 04 2003

STATUS

approved

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Last modified July 27 04:23 EDT 2021. Contains 346305 sequences. (Running on oeis4.)