

A280307


Numbers n such that 7^n  6^n is not squarefree, but 7^d  6^d is squarefree for every proper divisor d of n.


0




OFFSET

1,1


COMMENTS

a(5) >= 83.
Numbers n such that 7^n  6^n is not squarefree not divisible by any smaller number of the same form.
7^n  6^n is nonsquarefree if and only if n is divisible by a term of this sequence.  Jon E. Schoenfield, Jan 01 2017
The smallest squares of 7^n  6^n as defined above are 25, 169, 121, 289.  Robert Price, Mar 07 2017


LINKS

Table of n, a(n) for n=1..4.


EXAMPLE

20 is in this sequence because 7^20  6^20 = 43242508113549025 is not squarefree but 7^d  6^d is squarefree for every proper divisor d of 20 (i.e., for d = 1, 2, 4, 5, and 10): 7^1  6^1 = 1, 7^2  6^2 = 13, 7^4  6^4 = 1105, 7^5  6^5 = 13682, 7^10  6^10 = 222009013 are all squarefree.


CROSSREFS

Cf. A016169, A237043, A280203, A280208, A280209, A280302.
Sequence in context: A265401 A276503 A067065 * A101070 A219805 A219456
Adjacent sequences: A280304 A280305 A280306 * A280308 A280309 A280310


KEYWORD

nonn,more


AUTHOR

JuriStepan Gerasimov, Dec 31 2016


STATUS

approved



