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A020500 Cyclotomic polynomials at x=1. 18
0, 2, 3, 2, 5, 1, 7, 2, 3, 1, 11, 1, 13, 1, 1, 2, 17, 1, 19, 1, 1, 1, 23, 1, 5, 1, 3, 1, 29, 1, 31, 2, 1, 1, 1, 1, 37, 1, 1, 1, 41, 1, 43, 1, 1, 1, 47, 1, 7, 1, 1, 1, 53, 1, 1, 1, 1, 1, 59, 1, 61, 1, 1, 2, 1, 1, 67, 1, 1, 1, 71, 1, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also the greatest common divisor of the prime factors of n. - Peter Luschny, Mar 22 2011

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000

Yves Gallot, Cyclotomic polynomials and prime numbers

Bartlomiej Bzdega, Andres Herrera-Poyatos, Pieter Moree, Cyclotomic polynomials at roots of unity, arXiv:1611.06783 [math.NT], 2016. See Lemma 19.

Index entries for cyclotomic polynomials, values at X

FORMULA

a(1) = 0; for n > 1, a(n) = gcd(lpf(n),gpf(n)), by Gallot's theorem 1.4. - Thomas Ordowski, May 04 2013

For n > 2, a(n) = lcm(1,2,..,n)/lcm(1,..,n-1). - Thomas Ordowski, Nov 01 2013

MAPLE

with(numtheory, cyclotomic); f := n->subs(x=1, cyclotomic(n, x)); seq(f(i), i=0..64);

A020500 := n -> igcd(op(numtheory[factorset](n))):

seq(A020500(i), i=1..73); # Peter Luschny, Mar 22 2011

MATHEMATICA

Table[ Cyclotomic[n, 1], {n, 1, 73}] (* Jean-Fran├žois Alcover, Jan 10 2013 *)

PROG

(PARI) a(n) = polcyclo(n, 1); \\ Michel Marcus, Oct 23 2015

(PARI) a(n) = if (n==1, 0, if (isprimepower(n, &p), p, 1)); \\ Michel Marcus, Nov 23 2016

CROSSREFS

Apart from initial zero, same as A014963.

Cf. A007947.

Sequence in context: A214056 A014973 A276835 * A014963 A157753 A099636

Adjacent sequences:  A020497 A020498 A020499 * A020501 A020502 A020503

KEYWORD

nonn,easy,nice

AUTHOR

Simon Plouffe

STATUS

approved

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Last modified March 26 10:42 EDT 2017. Contains 284111 sequences.