A227731 Doubly 3-densely divisible numbers.

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

Offset

1,2

Comments

Numbers n such that for each d | n, there is some 3-densely 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[i-1], return(0))); 1
is(n)=my(d=select(k->dense(k, 3), divisors(n))); if(!#d||3*d[#d]<n, return(0)); for(i=2, #d, if(d[i]>3*d[i-1], 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