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

%I

%S 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,

%T 14,20,14,10,16,10,24,22,20,11,12,13,28,16,22,18,26,38,22,13,24,14,18,

%U 36,18,16,17,18,38,32,28,32,16,30,24,34,20,48,38,17

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

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

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

%o (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

%Y Cf. A224748, A224908.

%K nonn

%O 1,5

%A _Jayanta Basu_, Apr 22 2013

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Last modified January 24 01:05 EST 2020. Contains 331178 sequences. (Running on oeis4.)