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%I #52 Jul 19 2020 18:25:36
%S 0,0,1,1,2,2,1,1,4,2,2,4,3,2,4,3,4,3,4,4,6,3,4,5,3,5,5,4,3,6,4,7,5,4,
%T 6,5,7,9,7,5,6,5,6,6,8,5,7,9,5,6,7,5,7,7,9,10,3,11,8,11,6,9,8,12,8,9,
%U 7,10,9,7,8,8,6,14,8,10,11,11,12,11,7,7
%N Given n-th prime p, a(n) = number of primes of the form p * q - 2 where q is any prime < p.
%C Very similar to A103960. - _T. D. Noe_, Apr 18 2013
%C a(A137291(n)) = A103960(A137291(n)) - 1. - _Reinhard Zumkeller_, Jul 30 2015
%H Reinhard Zumkeller, <a href="/A210481/b210481.txt">Table of n, a(n) for n = 1..1000</a>
%t Table[p = Prime[n]; c = 0; Do[If[PrimeQ[p*Prime[i] - 2], c = c + 1], {i, n - 1}]; c, {n, 82}]
%t Table[With[{pr=Prime[Range[n]]},Count[Most[pr]Last[pr]-2,_?PrimeQ]],{n,90}] (* _Harvey P. Dale_, Jul 19 2020 *)
%o (Haskell)
%o a210481 n = sum [a010051' $ p * q - 2 |
%o let p = a000040 n, q <- takeWhile (< p) a000040_list]
%o -- _Reinhard Zumkeller_, Jul 30 2015
%Y Cf. A103960, A224748.
%Y Cf. A010051, A000040, A103960, A137291.
%K nonn
%O 1,5
%A _Jayanta Basu_, Apr 18 2013
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