A110559 Least j such that j*n^2 -1 and j*n^2 +1 are twin primes.

4, 1, 2, 12, 6, 2, 18, 3, 10, 6, 12, 3, 12, 18, 18, 57, 12, 5, 120, 12, 2, 3, 132, 2, 42, 3, 58, 45, 12, 7, 72, 15, 10, 3, 6, 2, 60, 30, 12, 3, 168, 2, 192, 18, 2, 33, 48, 10, 138, 39, 8, 63, 42, 22, 60, 42, 32, 3, 120, 6, 90, 18, 40, 165, 204, 7, 90, 18, 70, 6, 72, 27, 30, 15, 6, 18

Offset

1,1

Comments

Define Sj=sum of j(n) for n=1 to N. Define Sn=sum of (2*log(n))^2 for n=1 to N. As N increases Sj/Sn tends to 0.6. - Pierre CAMI, Dec 13 2011

Links

Pierre CAMI, Table of n, a(n) for n = 1..10000

Example

12*4*4-1=191, 191 and 193 are twin primes so a(4)=12.

Prog

(PARI) a(n) = my(j=1); while (!(isprime(p=j*n^2-1) && isprime(p+2)), j++); j; \\ Michel Marcus, Sep 17 2019

Crossrefs

Cf. A231819.

Sequence in context: A024569 A206692 A159756 * A365455 A030441 A298570

Adjacent sequences: A110556 A110557 A110558 * A110560 A110561 A110562

Keyword

nonn

Author

Pierre CAMI, Sep 12 2005

Extensions

Extended by Ray Chandler, Sep 15 2005

Status

approved