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
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Mar 04 2003
STATUS
approved