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A138301
Number of integers k < 10^n such that k*(k+1)-1 and k*(k+3)-1 are both first of twin primes.
0
1, 2, 4, 11, 37, 145, 673, 3748, 22875
OFFSET
1,2
EXAMPLE
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
CROSSREFS
Cf. A138303.
Sequence in context: A174107 A253927 A281481 * A367495 A173939 A328433
KEYWORD
nonn
AUTHOR
Pierre CAMI, Mar 14 2008
STATUS
approved