A344656 Number of odd composites <= 10^n.

1, 25, 332, 3771, 40408, 421502, 4335421, 44238545, 449152466, 4544947489, 45881945187, 462392087982, 4653934463161, 46795058249198, 470155429577331, 4720761658966075, 47376442842345767, 475260045712259140, 4765942332723655393, 47779180397439081160, 478872730513981268072, 4798532713310684093710

Offset

1,2

Links

Table of n, a(n) for n=1..22.

Formula

a(n) = 10^n/2 - A006880(n).

Example

a(1) = 1 because 9 is the only odd composite number <= 10^1.

Mathematica

Table[Length@Select[Range[2, 10^n], OddQ@#&&!PrimeQ@#&], {n, 7}]
(* or *)
Table[10^n/2-PrimePi[10^n], {n, 10}]

Crossrefs

Cf. A071904, A006880.

Sequence in context: A162702 A010977 A022589 * A199657 A094730 A265930

Adjacent sequences: A344653 A344654 A344655 * A344657 A344658 A344659

Keyword

nonn

Author

Giorgos Kalogeropoulos, May 26 2021

Status

approved