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A278617
Number of distinct odd primes less than or equal to 2n-3 that appear as a part in the partitions of 2n into two parts.
1
0, 0, 1, 2, 3, 3, 4, 5, 5, 6, 7, 7, 8, 8, 8, 9, 10, 10, 10, 11, 11, 12, 13, 13, 14, 14, 14, 15, 15, 15, 16, 17, 17, 17, 18, 18, 19, 20, 20, 20, 21, 21, 22, 22, 22, 23, 23, 23, 23, 24, 24, 25, 26, 26, 27, 28, 28, 29, 29, 29, 29, 29, 29, 29, 30, 30, 31, 31, 31
OFFSET
1,4
FORMULA
a(n) = pi(2n - 3) - 1 for n > 2 with a(1) = a(2) = 0.
MAPLE
with(numtheory): a:=n->`if`(n<3, 0, pi(2*n-3)-1): seq(a(n), n=1..100);
MATHEMATICA
Table[If[n < 3, 0, PrimePi[2n - 3] - 1], {n, 100}]
PROG
(Magma) [0, 0] cat [#PrimesUpTo(2*n-3)-1: n in [3..80]]; // Vincenzo Librandi, Nov 24 2016
CROSSREFS
Cf. A000720.
Essentially partial sums of A101264.
Sequence in context: A131138 A284724 A189579 * A194640 A353086 A189726
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Nov 23 2016
STATUS
approved