A219109 The smallest k such that prime(k) == -1 (mod n).

1, 2, 1, 2, 8, 3, 6, 4, 7, 8, 14, 5, 27, 6, 10, 11, 19, 7, 12, 8, 13, 14, 33, 9, 35, 27, 16, 23, 40, 10, 18, 11, 32, 19, 34, 20, 21, 12, 51, 22, 38, 13, 55, 14, 24, 33, 60, 15, 25, 35, 26, 27, 47, 16, 29, 39, 30, 40, 71, 17, 93, 18, 54, 31, 77, 32, 79, 19, 33, 34, 61, 20, 172, 21, 35, 36

Offset

1,2

Comments

Numbers n such that a(n) + 1 = a(n + 1) where the a(n)-th prime is not the smaller prime in a twin prime pair: 1, 3, 122, 267, 356, 362, 392, 403, 416, 446, 514, ....

Primes p(n) such that p is not -1 mod n for all prime p < p(n): 2, 3, 11, 31, 41, 59, 83, 97, 101, 109, 167, 191, 211, 277, 283, 313, 331, 367, 419,... Also primes p(n) such that p(n) <= A038700(n).

Links

Paolo P. Lava, Table of n, a(n) for n = 1..1000

Formula

a(n) = A000720(A038700(n)). - Joerg Arndt, Apr 16 2013

Example

For n = 11, we see that the 14th prime (43), modulo 11 is 10, or -1, so a(11) = 14.

Prog

(PARI) a(n)=forstep(t=n-1, n^99, n, if(isprime(t), return(primepi(t)))) \\ Charles R Greathouse IV, Mar 17 2014

Crossrefs

Cf. A038700, A221861.

Sequence in context: A208747 A334729 A221878 * A137305 A282885 A242841

Adjacent sequences: A219106 A219107 A219108 * A219110 A219111 A219112

Keyword

nonn

Author

Irina Gerasimova, Apr 11 2013

Status

approved