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A000423 a(n) is smallest number > a(n-1) of form a(i)a(j), i<j<n. 4
2, 3, 6, 12, 18, 24, 36, 48, 54, 72, 96, 108, 144, 162, 192, 216, 288, 324, 384, 432, 486, 576, 648, 768, 864, 972, 1152, 1296, 1458, 1536, 1728, 1944, 2304, 2592, 2916, 3072, 3456, 3888, 4374, 4608, 5184, 5832, 6144, 6912, 7776, 8748, 9216, 10368, 11664 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Main entry for this sequence is A033845, which is this sequence starting at 6. [Charles R Greathouse IV, Feb 27 2012]

REFERENCES

Amarnath Murthy, The sum of the reciprocals of the Smarandache multiplicative sequence, (to be published in Smarandache Notions Journal).

F. Smarandache, "Properties of the Numbers", University of Craiova Archives, 1975; Arizona State University Special Collections, Tempe, AZ

M. Myers, Smarandache Multiplicative Numbers, in Memorables 1998, Bristol Banner Books, Bristol, p. 37, 1998.

LINKS

Table of n, a(n) for n=1..49.

F. Smarandache, Sequences of Numbers Involved in Unsolved Problems.

FORMULA

Sequence contains 2, 3 and all numbers of form 2^a*3^b where a >= 1 and b >= 1 (David W. Wilson).

MATHEMATICA

a[1] = 2; a[2] = 3; a[n_] := a[n] = For[k = a[n - 1] + 1, True, k++, If[ AnyTrue[Table[a[i] a[j], {i, 1, n-2}, {j, i+1, n-1}] // Flatten, # == k& ], Return[k]]]; Table[an = a[n]; Print[an]; an, {n, 1, 50}] (* Jean-François Alcover, Feb 08 2016 *)

CROSSREFS

Subsequence of A003586, the 3-smooth numbers; A007335 and A033845 are subsequences.

Sequence in context: A174801 A280681 A093687 * A007335 A103070 A233422

Adjacent sequences:  A000420 A000421 A000422 * A000424 A000425 A000426

KEYWORD

nonn,easy

AUTHOR

R. Muller

EXTENSIONS

More terms from David W. Wilson Aug 15 1996.

STATUS

approved

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Last modified July 25 06:42 EDT 2017. Contains 289779 sequences.