1,2

3*4-1=11 11 and 13 twin primes, 3*6-1=17 17 and 19 twin primes a(1)=1

15*16-1=239 239 and 241 twin primes, 15*18-1=269 269 and 271 twin primes a(2)=2

Cf. A138303.

Sequence in context: A107378 A086611 A035098 this_sequence A118182 A107107 A101898

Adjacent sequences: A138298 A138299 A138300 this_sequence A138302 A138303 A138304

nonn

Pierre CAMI (pierrecami(AT)tele2.fr), Mar 14 2008