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A066665 a(n) = #{(x,y) | 0<=y<=x<=n and x+y is prime}. 0
1, 3, 5, 7, 9, 11, 14, 16, 19, 23, 27, 31, 35, 38, 42, 47, 52, 56, 61, 65, 70, 76, 82, 88, 94, 100, 107, 114, 121, 128, 136, 143, 150, 158, 166, 175, 185, 194, 203, 213, 223, 233, 243, 252, 262, 272, 282, 291, 301, 311, 322, 334, 346 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..52.

FORMULA

a(0) = 0, for n>0: a(n) = a(n-1) + A035250(n).

EXAMPLE

a(3)=5, as sums of (1,1), (2,0), (2,1), (3,0) and (3,2) give 5 primes.

CROSSREFS

Cf. A000720, A035250.

Sequence in context: A211218 A291839 A134917 * A278451 A175269 A318919

Adjacent sequences:  A066662 A066663 A066664 * A066666 A066667 A066668

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jan 07 2002

STATUS

approved

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Last modified May 8 07:02 EDT 2021. Contains 343653 sequences. (Running on oeis4.)