

A227731


Doubly 3densely divisible numbers.


2



1, 2, 3, 4, 6, 8, 9, 12, 16, 18, 20, 24, 27, 30, 32, 36, 40, 45, 48, 54, 60, 63, 64, 72, 80, 81, 84, 90, 96, 100, 108, 112, 120, 126, 128, 135, 140, 144, 150, 160, 162, 168, 176, 180, 189, 192, 200, 210, 216, 220, 224, 225, 240, 243, 252, 256, 264, 270, 280, 288, 300, 315
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

Numbers n such that for each d  n, there is some 3densely divisible (A196149) number d' such that d/3 < d' <= d.


LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Terence Tao, The distribution of primes in doubly densely divisible moduli


PROG

(PARI) dense(n, k)=my(d=divisors(n)); for(i=2, #d, if(d[i]>k*d[i1], return(0))); 1
is(n)=my(d=select(k>dense(k, 3), divisors(n))); if(!#d3*d[#d]<n, return(0)); for(i=2, #d, if(d[i]>3*d[i1], return(0))); 1


CROSSREFS

Cf. A227730, A196149.
Sequence in context: A010434 A074230 A064438 * A067947 A279542 A053640
Adjacent sequences: A227728 A227729 A227730 * A227732 A227733 A227734


KEYWORD

nonn


AUTHOR

Charles R Greathouse IV, Jul 23 2013


STATUS

approved



