A322982 If n is a noncomposite, then a(n) = 2*n - 1, otherwise a(n) = A032742(n), the largest proper divisor of n.

1, 3, 5, 2, 9, 3, 13, 4, 3, 5, 21, 6, 25, 7, 5, 8, 33, 9, 37, 10, 7, 11, 45, 12, 5, 13, 9, 14, 57, 15, 61, 16, 11, 17, 7, 18, 73, 19, 13, 20, 81, 21, 85, 22, 15, 23, 93, 24, 7, 25, 17, 26, 105, 27, 11, 28, 19, 29, 117, 30, 121, 31, 21, 32, 13, 33, 133, 34, 23, 35, 141, 36, 145, 37, 25, 38, 11, 39, 157, 40, 27, 41, 165, 42, 17, 43, 29

Offset: 1

Author

Antti Karttunen, Jan 03 2019

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A010051, A020639, A032742, A087717.

Programs

Mathematica

Array[If[CompositeQ@ #, Divisors[#][[-2]], 2 # - 1] &, 87] (* Michael De Vlieger, Jan 03 2019 *)

PARI

A322982(n) = if((1==n)||isprime(n),n+n-1,n/vecmin(factor(n)[,1]));

Formula

If A010051(n) == 1, a(n) = 2*n - 1, otherwise a(n) = A032742(n) = n/A020639(n).