A120942 3-smooth numbers 2^i*3^j where i and j are regular 3-smooth numbers.

6, 12, 18, 24, 36, 48, 54, 72, 108, 144, 162, 192, 216, 324, 432, 576, 648, 768, 1296, 1458, 1536, 1728, 2304, 2916, 4608, 5184, 5832, 6912, 11664, 12288, 13122, 13824, 20736, 26244, 36864, 39366, 41472, 46656, 52488, 78732, 104976, 110592, 157464

Offset

1,1

Links

Table of n, a(n) for n=1..43.

Example

54 is in the list because it is 2^1*3^3 and 1 and 3 are 3-smooth numbers.

Maple

interface(prettyprint=0) ; isA003586 := proc(n) local ifa, f, bas ; ifa := op(2, ifactors(n)) ; for f from 1 to nops(ifa) do bas := op(1, op(f, ifa)) ; if bas > 3 then RETURN(false) ; fi ; od ; RETURN(true) ; end: isA120942 := proc(n) local ifa, f, bas, expo ; ifa := op(2, ifactors(n)) ; if nops(ifa) <> 2 then RETURN(false) ; fi ; for f from 1 to nops(ifa) do bas := op(1, op(f, ifa)) ; if bas > 3 then RETURN(false) ; else expo := op(2, op(f, ifa)) ; if not isA003586(expo) then RETURN(false) ; fi ; fi ; od ; RETURN(true) ; end: for n from 2 to 40000 do if isA120942(n) then printf("%d, ", n) ; fi ; od; # R. J. Mathar, Aug 23 2006

Crossrefs

Cf. A003586.

Sequence in context: A033845 A187778 A344471 * A147306 A359957 A031478

Adjacent sequences: A120939 A120940 A120941 * A120943 A120944 A120945

Keyword

nonn

Author

Ben Paul Thurston, Aug 18 2006

Extensions

Corrected and extended by Ray Chandler and R. J. Mathar, Aug 23 2006

Status

approved