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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A081330 Numbers that can be written as sum of two 3-smooth numbers. 8
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 70, 72, 73, 74, 75, 76, 78, 80, 81, 82 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A081326(a(n)) > 0; complement of A081329.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Ivars Peterson, Medieval Harmony. [Broken link]

Eric Weisstein's World of Mathematics, Smooth Number.

FORMULA

a(n) >> exp(n^(1/4)). - Charles R Greathouse IV, Aug 22 2011

MATHEMATICA

max = 100; Table[2^i *3^j + 2^k* 3^l, {i, 0, Log[2, max] // Ceiling}, {j, 0, Log[3, max] // Ceiling}, {k, 0, Log[2, max] // Ceiling}, {l, 0, Log[3, max] // Ceiling}] // Flatten // Union // Select[#, # <= max &] & (* Jean-Fran├žois Alcover, Sep 10 2017 *)

PROG

(PARI) list(lim)=my(v=List(), u=v, N); for(n=0, log(lim\1+.5)\log(3), N=3^n; while(N<=lim, listput(v, N); N<<=1)); v=Set(v); for(i=1, #v, for(j=i, #v, N=v[i]+v[j]; if(N>lim, break); listput(u, N))); Set(u) \\ Charles R Greathouse IV, Sep 07 2014

CROSSREFS

Cf. A003586, A081332, A081333, A081327, A081328.

Sequence in context: A132264 A214922 A004830 * A080682 A182049 A038770

Adjacent sequences:  A081327 A081328 A081329 * A081331 A081332 A081333

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 19 2003

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 16 00:25 EDT 2018. Contains 313782 sequences. (Running on oeis4.)