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A070776 Numbers n such that number of terms in the n-th cyclotomic polynomial equals largest prime factor of n. 15
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 34, 36, 37, 38, 40, 41, 43, 44, 46, 47, 48, 49, 50, 52, 53, 54, 56, 58, 59, 61, 62, 64, 67, 68, 71, 72, 73, 74, 76, 79, 80, 81, 82, 83, 86, 88, 89, 92, 94, 96, 97, 98, 100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that A051664(n) = A006530(n).

This is also numbers in the form of 2^i*p^j, i>=0 and j>=0, p is an odd prime number. - Lei Zhou, Feb 18 2012

From Zhou's formulation (where the exponents i and j should actually have been specified as i>0 OR j>0, to exclude 1) it follows that this is a subsequence of A324109. It also follows that A005940(a(n)) = A324106(a(n)) for all n >= 1.- Antti Karttunen, Feb 15 2019

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

EXAMPLE

n=10: Cyclotomic[10,x]=1-x+x^2-x^3+x^4 with 5 terms [including 1] which equals largest prime factor (5) of 10=n.

MATHEMATICA

Select[Range[1000], (a=FactorInteger[#]; b=Length[a]; (b==1)||((b==2)&&(a[[1]][[1]]==2)))&] (* Lei Zhou, Feb 18 2012 *)

PROG

(PARI)

A006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1); \\ From A006530.

A051664(n) = length(select(x->x!=0, Vec(polcyclo(n)))); \\ After program in A051664

A070536(n) = (A051664(n) - A006530(n));

isA070776(n) = (!A070536(n)); \\ Antti Karttunen, Feb 15 2019

k=0; n=0; while(k<10000, n++; if(isA070776(n), k++; write("b070776.txt", k, " ", n)));

CROSSREFS

Positions of zeros in A070536.

Cf. A005940, A006530, A051664, A070537 (complement), A324106, A324109, A324111.

Sequence in context: A075592 A285801 A324109 * A320230 A076564 A325044

Adjacent sequences:  A070773 A070774 A070775 * A070777 A070778 A070779

KEYWORD

nonn,easy

AUTHOR

Labos Elemer, May 07 2002

STATUS

approved

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Last modified November 22 08:33 EST 2019. Contains 329389 sequences. (Running on oeis4.)