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a(n) = n - (largest nontrivial divisor of n, or 0 if there is none).
2

%I #17 Aug 21 2023 08:25:27

%S 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,

%T 14,29,15,31,16,22,17,28,18,37,19,26,20,41,21,43,22,30,23,47,24,42,25,

%U 34,26,53,27,44,28,38,29,59,30,61,31,42,32,52,33,67,34,46,35

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

%F a(n) = n - A032742(n) if n is composite, n otherwise. - _Jon E. Schoenfield_, Jul 21 2023

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

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

%o (Python)

%o from sympy import isprime, primefactors

%o def A364391(n): return n if n==1 or isprime(n) else n-n//min(primefactors(n)) # _Chai Wah Wu_, Aug 20 2023

%Y Cf. A032742, A060681.

%K nonn

%O 1,2

%A _Todor Szimeonov_, Jul 21 2023