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A038377 Number of odd nonprimes <= (2n+1)^2. 1
1, 2, 5, 11, 20, 32, 47, 66, 85, 110, 137, 167, 200, 237, 276, 320, 365, 414, 467, 522, 579, 643, 708, 777, 845, 924, 997, 1080, 1169, 1255, 1343, 1437, 1536, 1637, 1741, 1847, 1961, 2075, 2187, 2311, 2435, 2560, 2691, 2826, 2962, 3104, 3249, 3393, 3543 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..49.

FORMULA

For n>=1, a(n) = 2n^2+2n+2-PrimePi[(2n+1)^2] = A051890(n)-A000720((2n+1)^2). - Zak Seidov, Mar 03 2008

MATHEMATICA

nn=20001; With[{onps=Complement[Range[1, nn, 2], Prime[Range[PrimePi[nn+1]]]]}, Table[Count[onps, _?(#<=(2n+1)^2&)], {n, 0, 60}]]  (* Harvey P. Dale, Apr 13 2011 *)

CROSSREFS

A037040(n) + 1.

Cf. A000720, A051890.

Sequence in context: A093871 A033263 A139482 * A261227 A022908 A256310

Adjacent sequences:  A038374 A038375 A038376 * A038378 A038379 A038380

KEYWORD

nonn

AUTHOR

N. J. A. Sloane and Erich Friedman

STATUS

approved

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Last modified August 26 00:35 EDT 2019. Contains 326324 sequences. (Running on oeis4.)