A364391 a(n) = n - (largest nontrivial divisor of n, or 0 if there is none).

1, 2, 3, 2, 5, 3, 7, 4, 6, 5, 11, 6, 13, 7, 10, 8, 17, 9, 19, 10, 14, 11, 23, 12, 20, 13, 18, 14, 29, 15, 31, 16, 22, 17, 28, 18, 37, 19, 26, 20, 41, 21, 43, 22, 30, 23, 47, 24, 42, 25, 34, 26, 53, 27, 44, 28, 38, 29, 59, 30, 61, 31, 42, 32, 52, 33, 67, 34, 46, 35

Offset: 1

Author

Todor Szimeonov, Jul 21 2023

Keywords

• nonn

Examples

			The largest nontrivial divisor of 6 is 3, so a(6) = 6 - 3 = 3.
		

Crossrefs

Cf. A032742, A060681.

Programs

Mathematica

a[n_] := n - If[CompositeQ[n], n/FactorInteger[n][[1, 1]], 0]; Array[a, 100] (* Amiram Eldar, Jul 22 2023 *)

Python

from sympy import isprime, primefactors
def A364391(n): return n if n==1 or isprime(n) else n-n//min(primefactors(n)) # Chai Wah Wu, Aug 20 2023

Formula

a(n) = n - A032742(n) if n is composite, n otherwise. - Jon E. Schoenfield, Jul 21 2023