A224980 Number of primes of the form p-q-1 where q is any prime < p = prime(n).

0, 0, 1, 1, 3, 2, 4, 4, 5, 4, 6, 8, 6, 8, 7, 6, 7, 12, 12, 10, 12, 14, 9, 8, 14, 12, 16, 11, 16, 14, 20, 14, 10, 16, 10, 24, 22, 20, 11, 12, 13, 28, 16, 22, 18, 26, 38, 22, 13, 24, 14, 18, 36, 18, 16, 17, 18, 38, 32, 28, 32, 16, 30, 24, 34, 20, 48, 38, 17

Offset

1,5

Links

Table of n, a(n) for n=1..69.

Example

For n=5, p=11, there are a(5)=3 solutions: 11-3-1=7, 11-5-1=5, and 11-7-1=3.

Mathematica

Table[p = Prime[n]; c = 0; i = 1; While[i < n, If[PrimeQ[p - Prime[i] - 1], c = c + 1]; i++]; c, {n, 69}]

Prog

(PARI) a(n)=my(p=prime(n), s); forprime(q=2, p-1, s+=isprime(p-q-1)); s \\ Charles R Greathouse IV, Apr 22 2013

Crossrefs

Cf. A224748, A224908.

Sequence in context: A321232 A326015 A078822 * A368677 A154392 A069745

Adjacent sequences: A224977 A224978 A224979 * A224981 A224982 A224983

Keyword

nonn

Author

Jayanta Basu, Apr 22 2013

Status

approved