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A186928 Greater of two consecutive 3-smooth numbers having no common divisors. 3
2, 3, 4, 9, 32, 256, 2187, 531441, 134217728, 70368744177664, 36893488147419103232, 19383245667680019896796723, 713623846352979940529142984724747568191373312, 13803492693581127574869511724554050904902217944340773110325048447598592 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) = A003586(A186771(n) + 1); A186927(n) = A003586(A186771(n));

also a subsequence of A006899: all terms are either powers of 2 or of 3.

LINKS

Table of n, a(n) for n=1..14.

MATHEMATICA

smoothNumbers[p_, max_] := Module[{a, aa, k, pp, iter}, k = PrimePi[p]; aa = Array[a, k]; pp = Prime[Range[k]]; iter = Table[{a[j], 0, PowerExpand @ Log[pp[[j]], max/Times @@ (Take[pp, j - 1]^Take[aa, j - 1])]}, {j, 1, k}]; Table[Times @@ (pp^aa), Sequence @@ iter // Evaluate] // Flatten // Sort]; sn = smoothNumbers[3, 10^100]; Reap[For[i = 1, i <= Length[sn] - 1, i++, If[CoprimeQ[sn[[i]], sn[[i + 1]]], Sow[sn[[i + 1]]]]]][[2, 1]] (* Jean-Fran├žois Alcover, Nov 11 2016 *)

CROSSREFS

Cf. A186711.

Sequence in context: A059972 A245930 A086432 * A076018 A076017 A245366

Adjacent sequences:  A186925 A186926 A186927 * A186929 A186930 A186931

KEYWORD

nonn

AUTHOR

Charles R Greathouse IV and Reinhard Zumkeller, Mar 01 2011

STATUS

approved

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Last modified February 21 11:53 EST 2017. Contains 282443 sequences.