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 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A086424 Numbers needed to generate all other natural numbers, only allowing multiplication and addition. Each number can be used only once. 0
 1, 2, 4, 11, 25, 64, 171, 569, 3406, 27697, 243374, 1759619, 28381401, 222323189, 3416307938 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) >= 2a(n-1). - Charles R Greathouse IV, Jun 17 2013 EXAMPLE 10 is not in the sequence because (4+1)*2 = 10. 11 is in the sequence because there is no way to get 11 by using the earlier terms. 509 is not in the sequence because 509 = (1+25)*(2+11)+171. PROG (PARI) Ww(v)=if(#v==2, return([v[1], v[2], v[1]+v[2], v[1]*v[2]])); my(V=[], t); for(i=1, #v-1, for(j=i+1, #v, t=vecextract(v, 2^#v-1-2^(i-1)-2^(j-1)); V=concat(V, concat(Ww(concat(t, v[i]+v[j])), Ww(concat(t, v[i]*v[j]))))); V=vecsort(V, , 8)); V a=[1, 2, 4]; for(n=3, 9, V=Ww(a); for(i=2*a[#a], #V, if(V[i]>i, print(a=concat(a, i)); break))) \\ Charles R Greathouse IV, Jun 17 2013 CROSSREFS Sequence in context: A100550 A329707 A071973 * A122121 A080009 A159336 Adjacent sequences: A086421 A086422 A086423 * A086425 A086426 A086427 KEYWORD more,nonn,nice AUTHOR Arno Bouwes (acbouwes(AT)hotmail.com), Sep 08 2003 EXTENSIONS Corrected and extended by Don Reble, Sep 21, 2003 Two more terms from Jon E. Schoenfield, Aug 24 2009 a(13)-a(15) from Giovanni Resta, Jun 22 2013 STATUS approved

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

Last modified December 7 17:25 EST 2022. Contains 358668 sequences. (Running on oeis4.)