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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A116486 Numbers k such that both k and k + 1 are logarithmically smooth. 3
 8, 24, 80, 125, 224, 2400, 3024, 4224, 4374, 6655, 9800, 10647, 123200, 194480, 336140, 601425, 633555, 709631, 5142500, 5909760, 11859210, 1611308699 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS N is logarithmically smooth if its largest prime factor p <= ceiling(log_2(n)). Is the sequence finite? No more terms with largest prime factor <= 47. - Joerg Arndt, Jul 02 2012 LINKS Discussion titled Special Smooth numbers, (postings in mersenneforum.org), starting March 20 2006. EXAMPLE 125 is in the sequence because 125 = 5 * 5 * 5, 126 = 2 * 3 * 3 * 7; no prime factor is greater than ceiling(log_2(125)) = 7. MATHEMATICA logCeilSmoothQ[n_, b_:E] := FactorInteger[n][[-1, 1]] <= Ceiling[Log[b, n]]; Select[Range[10000], logCeilSmoothQ[#, 2] && logCeilSmoothQ[# + 1, 2] &] (* Alonso del Arte, Nov 27 2019 *) PROG (PARI) fm=97; /* max factor for factorizing, 2^97 >= searchlimit */ lpf(n)={ vecmax(factor(n, fm)[, 1]) } /* largest prime factor */ lsm(n)=if ( lpf(n)<=#binary(n-1), 1, 0 ); /* whether log-smooth, for n>=2 */ n0=3; /* lower search limit */ l1=lsm(n0-1); { for (n=n0, 10^10, l0 = lsm(n); if ( l0 && l1, print1(n-1, ", ") ); l1 = l0; ); } /* Joerg Arndt, Jul 02 2012 */ CROSSREFS Sequence in context: A303402 A078158 A221906 * A179609 A241690 A141317 Adjacent sequences: A116483 A116484 A116485 * A116487 A116488 A116489 KEYWORD nonn,hard,more AUTHOR Harsh R. Aggarwal, Mar 20 2006 EXTENSIONS Edited by Don Reble, Apr 07 2006 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 March 25 07:22 EDT 2023. Contains 361511 sequences. (Running on oeis4.)