A037040 Number of odd nonprimes < (2n+1)^2.

0, 1, 4, 10, 19, 31, 46, 65, 84, 109, 136, 166, 199, 236, 275, 319, 364, 413, 466, 521, 578, 642, 707, 776, 844, 923, 996, 1079, 1168, 1254, 1342, 1436, 1535, 1636, 1740, 1846, 1960, 2074, 2186, 2310, 2434, 2559, 2690, 2825, 2961, 3103, 3248, 3392, 3542

Offset: 0

Author

C. R. Christofferson (magpie56(AT)aol.com)

Keywords

• nonn

Examples

			The odd nonprimes < 25 are 1, 9, 15 and 21, so a(2) = 4.
		

References

• C. R. Christofferson, Unpublished notes, 15219 Wickmere, Houston, TX 77062, [phone].

Links

• Amiram Eldar, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A038377.

Programs

Mathematica

a[n_] := 2*n^2 + 2*n + 1 - PrimePi[(2*n + 1)^2]; a[0] = 0; Array[a, 61, 0] (* Amiram Eldar, Sep 06 2024 *)

PARI

a(n) = if(n == 0, 0, 2*n^2 + 2*n + 1 - primepi((2*n + 1)^2)); \\ Amiram Eldar, Sep 06 2024

Formula

a(n) = A038377(n) - 1.