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A052128 Largest factor of n that is coprime to a larger factor of n. 5
1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 3, 1, 1, 2, 1, 4, 3, 2, 1, 3, 1, 2, 1, 4, 1, 5, 1, 1, 3, 2, 5, 4, 1, 2, 3, 5, 1, 6, 1, 4, 5, 2, 1, 3, 1, 2, 3, 4, 1, 2, 5, 7, 3, 2, 1, 5, 1, 2, 7, 1, 5, 6, 1, 4, 3, 7, 1, 8, 1, 2, 3, 4, 7, 6, 1, 5, 1, 2, 1, 7, 5, 2, 3, 8, 1, 9, 7, 4, 3, 2, 5, 3, 1, 2, 9, 4, 1, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

Least k > 0 such that the resultant of the k-th cyclotomic polynomial and the n-th cyclotomic polynomial is not 1. - Benoit Cloitre, Oct 13 2002

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

a(6) = 6 / 3^1 = 2.

MATHEMATICA

Table[best = 1; d = Divisors[n]; While[Length[d] > 1, e = d[[1]]; d = Rest[d]; If[Min[GCD[e, d]] == 1, best = e]]; best, {n, 102}] (* T. D. Noe, Aug 23 2013 *)

PROG

(PARI) a(n) = my(i, j, d = divisors(n)); forstep (i = #d-1, 1, -1, for (j = i+1, #d, if (gcd(d[i], d[j]) == 1, return (d[i])))); 1 \\ Michel Marcus, Aug 22 2013

(PARI) a(n)=my(f=factor(n), v=[1]); for(i=1, #f~, v=concat(v, f[i, 1]^f[i, 2] *v)); v=vecsort(v); forstep(i=#v\2, 2, -1, for(j=i+1, #v-1, if(gcd(v[i], v[j])==1, return(v[i])))); 1 \\ Charles R Greathouse IV, Aug 22 2013

CROSSREFS

Cf. A054372.

Sequence in context: A284556 A025865 A085091 * A284600 A114536 A330692

Adjacent sequences:  A052125 A052126 A052127 * A052129 A052130 A052131

KEYWORD

nonn

AUTHOR

James A. Sellers, Jan 21 2000

EXTENSIONS

Terms corrected by Charles R Greathouse IV, Aug 22 2013

STATUS

approved

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Last modified September 22 03:21 EDT 2020. Contains 337289 sequences. (Running on oeis4.)