

A070776


Numbers k such that number of terms in the kth cyclotomic polynomial is equal to the largest prime factor of k.


20



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
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OFFSET

1,1


COMMENTS

Numbers k such that A051664(k) = A006530(k).
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
Also from Zhou's formulation, the union (disjoint) of A000079\{1} and A336101.  Peter Munn, Jul 16 2020
Numbers k>=2 such that A078701(k) = A299766(k).  JuriStepan Gerasimov, Jun 02 2021


LINKS

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


EXAMPLE

n=10: Cyclotomic[10,x]=1x+x^2x^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, A061345, A070537 (complement), A324106, A324111.
Subsequence of A324109.
Subsequences: A000079\{1}, A336101.
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



