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A227898 Number of primes p < n with p + 6 and n + (n - p)^2 both prime. 4
0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 4, 3, 2, 2, 3, 3, 3, 3, 3, 4, 4, 2, 2, 3, 3, 3, 2, 2, 5, 5, 2, 5, 4, 2, 4, 5, 2, 7, 5, 3, 4, 5, 3, 3, 4, 4, 3, 5, 4, 9, 9, 2, 5, 3, 4, 8, 6, 2, 5, 8, 3, 4, 7, 3, 10, 5, 2, 7, 4, 5, 10, 6, 4, 6, 6, 2, 6, 8, 3, 6, 5, 3, 6, 6, 5, 9, 4, 5, 7, 5, 4, 9, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,12
COMMENTS
Conjecture: (i) a(n) > 0 for all n > 5.
(ii) For any integer n > 5, there is a prime p with p + 6 and n*(n - p) - 1 both prime.
LINKS
Zhi-Wei Sun, Conjectures involving primes and quadratic forms, preprint, arXiv:1211.1588.
EXAMPLE
a(6) = 1 since 5, 5 + 6 = 11 and 6 + (6 - 5)^2 = 7 are all prime.
MATHEMATICA
a[n_]:=Sum[If[PrimeQ[Prime[i]+6]&&PrimeQ[n+(n-Prime[i])^2], 1, 0], {i, 1, PrimePi[n-1]}]
Table[a[n], {n, 1, 100}]
CROSSREFS
Sequence in context: A025834 A257379 A336456 * A035649 A278509 A094782
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Oct 14 2013
STATUS
approved

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Last modified March 28 15:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)