A378993 a(n) = n - omega(n), where omega = A001221.

1, 1, 2, 3, 4, 4, 6, 7, 8, 8, 10, 10, 12, 12, 13, 15, 16, 16, 18, 18, 19, 20, 22, 22, 24, 24, 26, 26, 28, 27, 30, 31, 31, 32, 33, 34, 36, 36, 37, 38, 40, 39, 42, 42, 43, 44, 46, 46, 48, 48, 49, 50, 52, 52, 53, 54, 55, 56, 58, 57, 60, 60, 61, 63, 63, 63, 66, 66

Offset: 1

Author

Torlach Rush, Dec 17 2024

Keywords

• nonn
• easy

Examples

			a(40) = 38, since 40 has two distinct prime divisors (2 and 5), and so 40 - 2 = 38.
a(41) = 40 also, since 41 is prime and therefore 41 - 1 = 40.
a(42) = 39, since 42 has three distinct prime divisors (2, 3, 7), and so 42 - 3 = 39.
		

Crossrefs

Cf. A001221, A229109.

Programs

Mathematica

a[n_]:=n-PrimeNu[n]; Array[a,68] (* Stefano Spezia, Dec 29 2024 *)

PARI

a(n) = n - omega(n);

Formula

a(n) = n - A001221(n).