A070537 - OEIS

A070537

Numbers k such that the k-th cyclotomic polynomial has more terms than the largest prime factor of k.

1, 15, 21, 30, 33, 35, 39, 42, 45, 51, 55, 57, 60, 63, 65, 66, 69, 70, 75, 77, 78, 84, 85, 87, 90, 91, 93, 95, 99, 102, 105, 110, 111, 114, 115, 117, 119, 120, 123, 126, 129, 130, 132, 133, 135, 138, 140, 141, 143, 145, 147, 150, 153, 154, 155, 156, 159, 161, 165

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

When (as at k=105) coefficients are not equal to 1 or -1, terms in C[k,x] are counted with multiplicity. This comment was left by the original author, but please see my comment in A070536. - Antti Karttunen, Feb 15 2019

Union of A324110 and A324111. - Antti Karttunen, Feb 15 2019

It appears that except for the initial 1, the terms are products of two or more distinct odd primes. - Enrique Navarrete, Oct 16 2022

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10001

FORMULA

Numbers n satisfying A070536(n) = A051664(n) - A006530(n) > 0.

EXAMPLE

k=21: Cyclotomic[21,x] = 1 - x + x^3 - x^4 + x^6 - x^8 + x^9 - x^11 + x^12 has 9 terms while the largest prime factor of 21 is 7; 9 > 7, so 21 is in the sequence.

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

isA070537(n) = (A051664(n) > A006530(n)); \\ Antti Karttunen, Feb 15 2019

for(n=1, 165, if(isA070537(n), print1(n, ", ")))

CROSSREFS

Cf. A006530, A051664, A070536, A070776 (complement), A324110, A324111.

Sequence in context: A026048 A195527 A047200 * A324110 A285800 A340380

Adjacent sequences: A070534 A070535 A070536 * A070538 A070539 A070540

KEYWORD

nonn

AUTHOR

Labos Elemer, May 03 2002

EXTENSIONS

Edited by N. J. A. Sloane, Nov 30 2022

STATUS

approved