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

1,1

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