OFFSET
1,1
EXAMPLE
a(2)=6: p(6)=13 and p(7)=17, the first cousin prime pair, p(8)=19 and p(9)=23, the second cousin prime pair.
MATHEMATICA
n=0 Do[If[Prime[k + 1] - Prime[k]==4&&Prime[k + 3] - Prime[k + 2]==4, n = n + 1; Print[n, " ", k]], {k, 1, 1700}] (* Vincenzo Librandi, Jul 03 2015 *)
PROG
(Magma) [n: n in [1..2000] | NthPrime(n+1)-NthPrime(n) eq 4 and NthPrime(n+3)-NthPrime(n+2) eq 4]; // Vincenzo Librandi, Jul 03 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Ray G. Opao, Jul 15 2004
STATUS
approved