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 A210469 a(n) = n - primepi(2n). 3
 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 5, 6, 7, 7, 8, 8, 8, 9, 9, 10, 11, 11, 12, 13, 13, 13, 14, 15, 15, 16, 16, 16, 17, 18, 18, 19, 19, 20, 21, 21, 22, 23, 24, 24, 25, 25, 25, 26, 26, 26, 27, 27, 28, 29, 30, 31, 32, 33, 33, 34, 34, 35, 36, 36, 36 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,8 COMMENTS The number of distinct odd composite parts appearing in the partitions of 2n into two parts. a(n) is the number of odd composite numbers up to 2*n-1. - Michel Marcus, Aug 05 2023 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..10000 Index entries for sequences related to partitions FORMULA a(n) = n - primepi(2n). EXAMPLE a(6) = 1 since 9 is the only odd composite number appearing in the partitions of 2*6 = 12 into two parts. For example, 12 = (1+11) = (2+10) = (3+9) = (4+8) = (5+7) = (6+6). Note that the numbers in the partitions with identical parts are counted only once. MAPLE with(numtheory); a:=n->n-pi(2*n); seq(a(k), k=1..70); MATHEMATICA Table[n - PrimePi[2 n], {n, 70}] (* Robert G. Wilson v, Jan 24 2013 *) PROG (PARI) a(n) = n - primepi(2*n); \\ Michel Marcus, Aug 05 2023 CROSSREFS Cf. A099802. See A224710 for a closely related sequence. Sequence in context: A194251 A029114 A224710 * A073174 A107631 A029098 Adjacent sequences: A210466 A210467 A210468 * A210470 A210471 A210472 KEYWORD nonn,easy AUTHOR Wesley Ivan Hurt, Jan 24 2013 STATUS approved

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Last modified September 17 08:27 EDT 2024. Contains 375986 sequences. (Running on oeis4.)