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A330558
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a(n) = number of primes p <= 2*n+1 with Delta(p) == 0 mod 4, where Delta(p) = nextprime(p) - p.
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5
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0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12
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OFFSET
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0,7
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LINKS
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MAPLE
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N:= 100: # for a(0)..a(N)
P:= select(isprime, [seq(i, i=3..nextprime(2*N+1), 2)]):
Delta:= P[2..-1]-P[1..-2] mod 4:
A:= Array(0..N): t:= 0: j:= 1:
for n from 0 to N do
m:= 2*n+1:
if m = P[j] then t:= t + charfcn[0](Delta[j]); j:= j+1 fi;
A[n]:= t
od:
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PROG
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(Magma) [#[p:p in PrimesInInterval(1, 2*n+1)| (NextPrime(p)-p) mod 4 eq 0]:n in [0..80]]; // Marius A. Burtea, Dec 31 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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