A107485 a(1) is the least k such that j(1) = k*2*3 - 1 is the lesser of a twin prime pair; then for n > 1, a(n) is the least k greater than a(n-1) such that j(n) = k*j(n-1)*(j(n-1)+2) - 1 is the lesser of a twin prime pair.

1, 12, 270, 402, 9396, 17490, 187932, 488214, 2936526, 7900764

Offset

1,2

Links

Table of n, a(n) for n=1..10.

Pierre CAMI, PFGW Script

Example

1*2*3 - 1 = 5, 5 and 7 twin primes, a(1) = 1.
12*5*7 - 1 = 419, 419 and 421 twin primes, a(2) = 12.
270*419*421 - 1 = 47627729, 47627729 and 4762731 twin primes, a(3) = 270.

Prog

(PARI) lista(nn) = {my(j=5, k=1, m); print1(k); for(n=2, nn, m=j*(j+2); j=k*m-1; while(ispseudoprime(j+=m)+ispseudoprime(j+2)<2, k++); print1(", ", k++)); } \\ Jinyuan Wang, Mar 05 2020

Crossrefs

Sequence in context: A068283 A003390 A239779 * A293270 A341815 A117415

Adjacent sequences: A107482 A107483 A107484 * A107486 A107487 A107488

Keyword

nonn,more

Author

Pierre CAMI, May 28 2005

Extensions

a(8) corrected by Jinyuan Wang, Mar 05 2020

Name clarified by Michel Marcus, Mar 07 2020

a(9)-a(10), computed by Pierre CAMI, added by Michel Marcus, Mar 08 2020

Status

approved