A221861 -id:A221861 - cp's OEIS frontend

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

Irina Gerasimova, Apr 11 2013

nonn

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).

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

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

Cf. A038700, A221861.

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

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

cp's OEIS Frontend

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

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