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A224980 Number of primes of the form p-q-1 where q is any prime < p = prime(n). 1
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 (list; graph; refs; listen; history; text; internal format)
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 * A154392 A069745 A112199

Adjacent sequences:  A224977 A224978 A224979 * A224981 A224982 A224983

KEYWORD

nonn

AUTHOR

Jayanta Basu, Apr 22 2013

STATUS

approved

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Last modified June 13 00:04 EDT 2021. Contains 344980 sequences. (Running on oeis4.)