A320276 a(n) is the smallest prime p such that there are n pairs of primes (i,j) with i < j < p and i*j == 1 mod p.

2, 5, 19, 61, 67, 127, 191, 263, 257, 313, 311, 569, 587, 457, 677, 499, 997, 1061, 967, 991, 853, 1153, 1399, 1321, 1381, 1733, 1669, 2143, 2137, 1637, 1993, 2029, 2843, 2609, 2179, 2749, 2393, 3467, 2939, 3221, 3229

Offset

0,1

Links

David A. Corneth, Table of n, a(n) for n = 0..10000 (first 1331 terms from Chai Wah Wu)

Example

There are no primes < 2, so a(0)=2.
The first time there is a pair of primes (i,j) less than some prime p with i*j == 1 mod p is when p=5 and i=2, j=3, so a(1)=5.
For n = 2 we take p = 19 and the pairs (3,13) and (7,11).

Prog

(PARI) nbpp(p) = {my(nb = 0); forprime(i=2, p-1, forprime(j=2, i-1, if ((i*j % p) == 1, nb ++); ); ); nb; }
a(n) = {my(p = 2); while (nbpp(p) != n, p = nextprime(p+1)); p; } \\ Michel Marcus, Nov 05 2018

Crossrefs

An inverse to A321005.

Sequence in context: A062666 A148431 A321006 * A148432 A047116 A148433

Adjacent sequences: A320273 A320274 A320275 * A320277 A320278 A320279

Keyword

nonn

Author

David James Sycamore, Oct 08 2018

Extensions

More terms from N. J. A. Sloane, Nov 02 2018

Status

approved