A065896 Number of composites <= 2*n.

0, 1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 14, 16, 18, 19, 20, 22, 24, 25, 27, 28, 29, 31, 32, 34, 36, 37, 39, 41, 42, 43, 45, 47, 48, 50, 51, 52, 54, 56, 57, 59, 60, 62, 64, 65, 67, 69, 71, 72, 74, 75, 76, 78, 79, 80, 82, 83, 85, 87, 89, 91, 93, 95, 96, 98, 99, 101, 103, 104, 105

Offset

1,3

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Formula

a(n) = A065855(2*n). - Reinhard Zumkeller, Oct 14 2014

Example

a(9) = 10, since 18 is the 10th composite number: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18.

Mathematica

Table[2*n-(PrimePi[2*n])-1, {n, 1, 128}]

Prog

(PARI) { for (n=1, 1000, f=2*n; a=f - primepi(f) - 1; write("b065896.txt", n, " ", a) ) } \\ Harry J. Smith, Nov 04 2009
(Haskell)
a065896 = a065855 . (* 2)  -- Reinhard Zumkeller, Oct 14 2014

Crossrefs

Cf. A002808, A000720, A005843, A065855.

Sequence in context: A305847 A376958 A248565 * A358215 A099308 A359544

Adjacent sequences: A065893 A065894 A065895 * A065897 A065898 A065899

Keyword

nonn

Author

Labos Elemer, Nov 28 2001

Extensions

More precise definition from Michel Marcus, Mar 07 2021~

Status

approved