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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
Sequence contains 2, 3 and all numbers of form 2^a*3^b where a >= 1 and b >= 1. - David W. Wilson, Aug 15 1996
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
FORMULA
Sum_{n>=1} 1/a(n) = 4/3. - Amiram Eldar, Jul 31 2022
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 (3-smooth numbers).
A007335 and A033845 are subsequences.
Sequence in context: A280681 A328899 A093687 * A007335 A309311 A361693
KEYWORD
nonn,easy
AUTHOR
R. Muller
EXTENSIONS
More terms from David W. Wilson, Aug 15 1996
STATUS
approved

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Last modified March 28 16:28 EDT 2024. Contains 371254 sequences. (Running on oeis4.)