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

1,1

Links

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

Example

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.

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 *)

Prog

(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

Crossrefs

Cf. A089090 (the 1st such composite).

Sequence in context: A143899 A154068 A309526 * A284119 A290377 A332767

Adjacent sequences: A126598 A126599 A126600 * A126602 A126603 A126604

Keyword

nonn

Author

Leroy Quet, Jan 06 2007

Extensions

Extended by Ray Chandler, Jan 08 2007

Status

approved