A140115 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A140115

a(n) is the number of numbers k between n^3 and (n + 1)^3 that are the product of 3 distinct primes.

0, 0, 0, 2, 7, 10, 16, 27, 32, 41, 53, 72, 76, 104, 104, 143, 137, 174, 203, 209, 241, 271, 280, 324, 360, 381, 391, 466, 497, 499, 545, 598, 646, 676, 737, 725, 818, 850, 930, 953, 948, 1055, 1113, 1151, 1221, 1301, 1294, 1394, 1425, 1520, 1589, 1657, 1694, 1766, 1801

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

OFFSET

0,4

LINKS

Table of n, a(n) for n=0..54.

EXAMPLE

a(3) = 2, counting 30 and 42 between 3^3 = 27 and 4^3 = 64.

a(4) = 7, counting 66, 70, 78, 102, 105, 110 and 114 between 4^3 = 64 and 5^3 = 125. - David A. Corneth, May 19 2018

PROG

(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim)^(1/3), forprime(q=p+1, sqrt(lim\p), t=p*q; forprime(r=q+1, lim\t, listput(v, t*r)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 20 2011 at A007304.

first(n) = {my(res = vector(n), l = list(n ^ 3), il = 1, ir = 4, ol = nl = 1); res[1] = 0; while(il <= #l, if(ir ^ 3 < l[il], ir++); res[ir]++; il++); res} \\ David A. Corneth, May 19 2018

CROSSREFS

Cf. A007304, A140114.

Sequence in context: A226830 A059316 A295825 * A294865 A105770 A240469

Adjacent sequences: A140112 A140113 A140114 * A140116 A140117 A140118

KEYWORD

easy,nonn

AUTHOR

Philippe Lallouet (philip.lallouet(AT)orange.fr), May 08 2008

EXTENSIONS

Corrected name, data and put more terms by David A. Corneth, May 19 2018

STATUS

approved