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A124201 a(n) = n-th positive integer from among those positive integers which are coprime to every noncomposite (1 or prime) which is < n and does not divide n. 0
1, 2, 5, 5, 13, 7, 23, 17, 27, 17, 43, 18, 59, 32, 43, 43, 79, 36, 97, 50, 71, 62, 113, 58, 125, 79, 109, 79, 157, 53, 173, 118, 131, 113, 167, 94, 211, 134, 167, 125, 239, 96, 257, 158, 191, 173, 281, 146, 283, 167, 237, 194, 331, 167, 295, 202, 267, 227, 373, 144 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For which n's are n and a(n) coprime?

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

The primes < 8 and coprime to 8 are 3, 5 and 7. The positive integers which are coprime to these primes (i.e. which are coprime to 3*5*7) are 1, 2, 4, 8, 11, 13, 16, 17, 19, ...a(8) is the 8th of these integers, which is 17.

MATHEMATICA

f[n_] := Block[{c = n, k = 0, p}, p = Times @@ Select[Range[n - 1], PrimeQ[ # ] && GCD[ #, n] == 1 &]; While[c > 0, k++; While[GCD[k, p] > 1, k++ ]; c--; ]; k]; Table[f[n], {n, 61}] (* Ray Chandler, Dec 11 2006 *)

CROSSREFS

Sequence in context: A138316 A183719 A239340 * A100953 A112835 A206625

Adjacent sequences:  A124198 A124199 A124200 * A124202 A124203 A124204

KEYWORD

nonn

AUTHOR

Leroy Quet, Dec 07 2006

EXTENSIONS

Extended by Ray Chandler, Dec 11 2006

STATUS

approved

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Last modified February 26 17:19 EST 2020. Contains 332293 sequences. (Running on oeis4.)