OFFSET
1,30
COMMENTS
LINKS
Zhi-Wei Sun, Table of n, a(n) for n = 1..10000
Zhi-Wei Sun, Conjectures involving primes and quadratic forms, arXiv:1211.1588.
Zhi-Wei Sun, Table of n, a(n) for n = 1..10^5.
EXAMPLE
a(20)=1 since 20=11+3*3 with 11-4 and 3+4 prime. a(28)=1 since 28=41-13 with 41-4 and 13+4 prime.
MATHEMATICA
c[n_]:=c[n]=If[Mod[n+2, 6]==0, 1, -1-Mod[n, 6]]; d[n_]:=d[n]=2+If[Mod[n+2, 6]>0, Mod[n, 6], 0]; a[n_]:=a[n]=Sum[If[PrimeQ[Prime[k]+4] == True && PrimeQ[n+c[n]Prime[k]] == True && PrimeQ[n+c[n]Prime[k]-4]==True, 1, 0], {k, 1, PrimePi[(n-1)/d[n]]}]; Do[Print[n, " ", a[n]], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Nov 13 2012
STATUS
approved