A227730 Doubly 2-densely divisible numbers.

1, 2, 4, 8, 12, 16, 24, 32, 36, 48, 60, 64, 72, 80, 96, 108, 112, 120, 128, 144, 160, 168, 180, 192, 216, 224, 240, 252, 256, 288, 300, 320, 324, 336, 360, 384, 396, 400, 420, 432, 448, 480, 504, 512, 528, 540, 560, 576, 600, 640, 648, 660, 672, 704, 720, 756, 768, 784

Offset

1,2

Comments

Numbers n such that for each d | n, there is some 2-densely divisible (A174973) number d' such that d/2 < 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, 2), divisors(n))); if(!#d||2*d[#d]<n, return(0)); for(i=2, #d, if(d[i]>2*d[i-1], return(0))); 1

Crossrefs

Cf. A227731, A174973.

Sequence in context: A047836 A325762 A231958 * A246692 A181824 A326677

Adjacent sequences: A227727 A227728 A227729 * A227731 A227732 A227733

Keyword

nonn

Author

Charles R Greathouse IV, Jul 23 2013

Status

approved