

A330561


a(n) = number of primes p <= prime(n) with Delta(p) == 0 mod 4, where Delta(p) = nextprime(p)  p.


10



0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 5, 5, 5, 5, 5, 6, 6, 6, 7, 7, 8, 9, 9, 10, 10, 11, 11, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 14, 14, 15, 16, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 21, 21, 21, 21, 21, 22, 22, 23, 23, 23, 24, 24, 25, 26, 27, 27, 27, 27, 27
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OFFSET

1,6


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


MAPLE

N:= 200: # for a(1)..a(N)
P:= [seq(ithprime(i), i=1..N+1)]:
Delta:= P[2..1]P[1..2] mod 4:
R:= map(charfcn[0], Delta):
ListTools:PartialSums(R); # Robert Israel, Dec 31 2019


PROG

(MAGMA) [#[p:p in PrimesInInterval(1, NthPrime(n))IsIntegral((NextPrime(p)p)/4)]:n in [1..80]]; // Marius A. Burtea, Dec 31 2019


CROSSREFS

Cf. A098059.
Sequences related to the differences between successive primes: A001223 (Delta(p)), A028334, A080378, A104120, A330556A330561.
Sequence in context: A196383 A074198 A196169 * A048688 A092695 A281687
Adjacent sequences: A330558 A330559 A330560 * A330562 A330563 A330564


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Dec 30 2019


STATUS

approved



