A126601 a(n) = n-th composite from among those composites which are coprime to n.

4, 15, 10, 25, 12, 77, 15, 39, 26, 69, 20, 121, 22, 81, 56, 69, 27, 161, 30, 121, 65, 105, 35, 205, 49, 119, 68, 141, 44, 391, 46, 123, 92, 141, 81, 287, 54, 153, 106, 213, 58, 425, 62, 185, 146, 177, 66, 343, 82, 259, 128, 209, 75, 385, 114, 253, 142, 215, 82, 671, 85

Offset: 1

Author

Leroy Quet, Jan 06 2007

Keywords

• nonn

Examples

			The composites which are coprime to 6 are: 25,35,49,55,65,77,85,...So a(6) is the 6th of these, which is 77.
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A089090 (the 1st such composite).

Programs

Mathematica

f[n_] := Block[{k = 1, c = n},While[c > 0,k++;While[PrimeQ[k] || GCD[k, n] > 1, k++ ];c--;];k];Table[f[n], {n, 61}] (* Ray Chandler, Jan 08 2007 *)

PARI

a(n) = {my(c=2, nb=0); while(nb != n, c++; if (!isprime(c) && (gcd(c,n)==1), nb++)); c;} \\ Michel Marcus, Sep 06 2019

Extensions

Extended by Ray Chandler, Jan 08 2007