1,1

Table of n, a(n) for n=1..12.

In the 100 first primes (up to and including 541) there are 49 twin primes: 3, 5, 7, 11, 13, 17, 19, 29, 31, 41, 43, 59, 61, 71, 73, 101, 103, 107, 109, 137, 139, 149, 151, 179, 181, 191, 193, 197, 199, 227, 229, 239, 241, 269, 271, 281, 283, 311, 313, 347, 349, 419, 421, 431, 433, 461, 463, 521, 523

Table[Count[Prime[Range[10^n]], _?(AnyTrue[#+{2, -2}, PrimeQ]&)], {n, 8}] (* The program uses the AnyTrue function from Mathematica version 10 *)

Cf. A001097, A001359, A006512.

Sequence in context: A037483 A188708 A317752 * A024106 A176626 A176674

Adjacent sequences: A273494 A273495 A273496 * A273498 A273499 A273500

nonn,more

Harvey P. Dale, May 23 2016

a(9)-a(11) from Giovanni Resta, May 23 2016

a(12) from Giovanni Resta, May 25 2016

approved