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A242802
Number of primes p < n such that n - p is a term of A242754.
1
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.
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
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, May 23 2014
STATUS
approved