OFFSET
0,9
LINKS
Eric Weisstein's World of Mathematics, Twin Primes
EXAMPLE
a(15) = 6 because we have [7, 5, 3], [7, 3, 5], [5, 7, 3], [5, 3, 7], [3, 7, 5] and [3, 5, 7].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 05 2020
STATUS
approved