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A330560 a(n) = number of primes p <= prime(n) with Delta(p) == 2 mod 4, where Delta(p) = nextprime(p) - p. 2
0, 1, 2, 2, 3, 3, 4, 4, 5, 6, 7, 7, 8, 8, 9, 10, 11, 12, 12, 13, 14, 14, 15, 15, 15, 16, 16, 17, 17, 18, 18, 19, 20, 21, 22, 23, 24, 24, 25, 26, 27, 28, 29, 29, 30, 30, 30, 30, 31, 31, 32, 33, 34, 35, 36, 37, 38, 39, 39, 40, 41, 42, 42, 43, 43, 44, 45, 46, 47, 47, 48, 48, 49, 50, 50, 51, 51, 51, 51, 52, 53, 54 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

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[2], Delta):

ListTools:-PartialSums(R); # Robert Israel, Dec 31 2019

PROG

(MAGMA) [#[p:p in PrimesInInterval(1, NthPrime(n))| (NextPrime(p)-p) mod 4 eq 2]:n in [1..90]]; // Marius A. Burtea, Dec 31 2019

CROSSREFS

Sequences related to the differences between successive primes: A001223 (Delta(p)), A028334, A080378, A104120, A330556-A330561.

Sequence in context: A137222 A077641 A329547 * A194210 A112672 A025765

Adjacent sequences:  A330557 A330558 A330559 * A330561 A330562 A330563

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 30 2019

STATUS

approved

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Last modified September 25 07:33 EDT 2020. Contains 337335 sequences. (Running on oeis4.)