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

1,5

Comments

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

Links

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

Example

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

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}]

Crossrefs

Cf. A000040, A242753, A242754, A242755.

Sequence in context: A316398 A183095 A304817 * A277561 A317684 A127973

Adjacent sequences: A242799 A242800 A242801 * A242803 A242804 A242805

Keyword

nonn

Author

Zhi-Wei Sun, May 23 2014

Status

approved