A242802 Number of primes p < n such that n - p is a term of A242754.

0, 0, 0, 1, 2, 2, 2, 2, 4, 2, 2, 2, 4, 3, 4, 3, 3, 3, 3, 5, 4, 3, 5, 5, 3, 4, 2, 3, 3, 4, 2, 3, 4, 5, 3, 4, 2, 3, 3, 5, 3, 5, 4, 7, 3, 3, 5, 7, 4, 7, 6, 4, 5, 9, 5, 5, 5, 5, 6, 9, 4, 5, 8, 6, 8, 6, 4, 6, 8, 5, 10, 7, 6, 8, 9, 5, 14, 10, 6, 7

Offset: 1

Author

Zhi-Wei Sun, May 23 2014

Keywords

• nonn

Comments

Conjecture: a(n) > 0 for all n > 3.

Examples

			a(4) = 1 since 2 is prime with 4 - 2 = 2 a term of A242754.
		

Links

• Zhi-Wei Sun, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A242753, A242754, A242755.

Programs

Mathematica

p[n_]:=PrimeQ[PowerMod[n,-1,Prime[n]]]
a[n_]:=Sum[Boole[p[n-Prime[k]]],{k,1,PrimePi[n-1]}]
Table[a[n],{n,1,80}]