login
This site is supported by donations to The OEIS Foundation.

 

Logo

Many excellent designs for a new banner were submitted. We will use the best of them in rotation.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A046308 Numbers that are divisible by exactly 7 primes counting multiplicity. 48
128, 192, 288, 320, 432, 448, 480, 648, 672, 704, 720, 800, 832, 972, 1008, 1056, 1080, 1088, 1120, 1200, 1216, 1248, 1458, 1472, 1512, 1568, 1584, 1620, 1632, 1680, 1760, 1800, 1824, 1856, 1872, 1984, 2000, 2080, 2187, 2208, 2268, 2352, 2368, 2376 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also called 7-almost primes. Products of exactly 7 primes (not necessarily distinct). - Jonathan Vos Post, Dec 11 2004

Also, positions of 7 in A001222. - Zak Seidov, Oct 14 2012

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Reference

FORMULA

Product p_i^e_i with sum e_i = 7.

a(n) ~ 720n log n / (log log n)^6. - Charles R Greathouse IV, May 06 2013

MATHEMATICA

Select[Range[900], Plus @@ Last /@ FactorInteger[ # ] == 7 &] - Vladimir Orlovsky, Apr 23 2008

PROG

(PARI) is(n)=bigomega(n)==7 \\ Charles R Greathouse IV, Mar 21 2013

CROSSREFS

Cf. A120048 (number of 7-almost primes <= 10^n).

Cf. A101605, A101606, A001222.

Sequences listing r-almost primes; that is the n such that A001222(n) = r: A000040 (r = 1), A001358 (r = 2), A014612 (r = 3), A014613 (r = 4), A014614 (r = 5), A046306 (r = 6), this sequence (r = 7), A046310 (r = 8), A046312 (r = 9), A046314 (r = 10), A069272 (r = 11), A069273 (r = 12), A069274 (r = 13), A069275 (r = 14), A069276 (r = 15), A069277 (r = 16), A069278 (r = 17), A069279 (r = 18), A069280 (r = 19), A069281 (r = 20). - Jason Kimberley, Oct 02 2011

Sequence in context: A114418 A046307 A036331 * A110290 A045028 A172421

Adjacent sequences:  A046305 A046306 A046307 * A046309 A046310 A046311

KEYWORD

nonn

AUTHOR

Patrick De Geest, Jun 15 1998.

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified April 24 12:03 EDT 2014. Contains 240983 sequences.