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A224965 Let p = prime(n). a(n) = number of primes q less than p, such that both p*q+p+q and p*q-p-q are primes. 4
0, 0, 2, 3, 1, 2, 2, 2, 1, 2, 1, 1, 3, 2, 1, 1, 1, 3, 2, 2, 1, 3, 1, 0, 4, 0, 1, 2, 5, 0, 2, 2, 1, 2, 2, 2, 1, 2, 2, 1, 1, 4, 2, 1, 0, 2, 5, 1, 1, 3, 1, 3, 3, 3, 0, 1, 2, 4, 1, 4, 4, 2, 2, 2, 6, 2, 5, 2, 3, 3, 2, 4, 5, 3, 2, 1, 3, 1, 3, 3, 3, 2, 2, 3, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..85.

EXAMPLE

For n=3, p=5, there are a(3)=2 solutions 2,3 since 5*2+5+2=17, 5*2-5-2=3 and 5*3+5+3=23, 5*3-5-3=7. Also for n=5, p=11, there is a(5)=1 solution in the form of 11*3+11+3=47, 11*3-11-3=19.

MATHEMATICA

Table[p = Prime[n]; c = 0; i = 1; While[i < n, q1 = p*Prime[i]; q2 = p + Prime[i]; If[PrimeQ[q1 + q2] && PrimeQ[q1 - q2], c = c + 1]; i++]; c, {n, 85}]

CROSSREFS

Cf. A224748, A224908, A224925, A224962.

Sequence in context: A128864 A106798 A214640 * A194298 A194306 A283325

Adjacent sequences:  A224962 A224963 A224964 * A224966 A224967 A224968

KEYWORD

nonn

AUTHOR

Jayanta Basu, Apr 21 2013

STATUS

approved

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Last modified April 25 12:19 EDT 2019. Contains 322456 sequences. (Running on oeis4.)