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Number of primes p such that n divided by p leaves a prime remainder.
7

%I #5 Dec 05 2013 19:55:21

%S 0,0,0,0,1,0,1,2,1,1,1,2,2,2,1,3,3,3,2,3,1,3,3,5,2,4,2,4,3,4,3,4,4,3,

%T 2,6,4,5,2,6,4,6,3,6,4,5,5,7,4,6,4,5,4,8,3,5,4,7,5,9,3,7,5,8,5,7,3,8,

%U 4,8,5,10,6,7,5,8,4,9,6,9,7,8,4,10,5,7,6,8,7,12,5,8,8,8,5,12,6,10,5,10,5

%N Number of primes p such that n divided by p leaves a prime remainder.

%C Is there any n > 6 such that a(n) =0 ?

%e a(17) = 3: there are 3 primes viz. 3, 5 and 7 which leave prime remainders on dividing 17.

%t Table[Count[PrimeQ[Table[Mod[w, Prime[j]], {j, 1, PrimePi[w]}]], True], {w, 1, 256}]

%Y Cf. A072531.

%K nonn

%O 1,8

%A _Amarnath Murthy_, Aug 01 2002

%E More terms from _Labos Elemer_, Aug 02 2002