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A182856
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a(0) = 1; for n > 0, a(n) = smallest positive integer whose prime signature contains, for k = 1 to n, exactly one positive number appearing exactly k times.
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2
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OFFSET
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0,2
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COMMENTS
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a(n) = smallest number m such that A181819(m) = A006939(n). a(n) belongs to A182855 iff n > 1.
Next term has 105 digits.
Smallest number k with A323022(k) = n, where A323022(m) is the number of distinct multiplicities in the prime signature of m. - Gus Wiseman, Jan 03 2019
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LINKS
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David A. Corneth, Table of n, a(n) for n = 0..12
D. Alpern, Factorization using the Elliptic Curve Method
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FORMULA
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Partial products of A113511.
log a(n) ~ (1/3) n^3 log n. [Charles R Greathouse IV, Jan 13 2012]
A001222(a(n)) = A000292(n). - Gus Wiseman, Jan 03 2019
a(0) = 1; a(n + 1) = A002110(binomial(n + 2, 2)) * a(n). - David A. Corneth, Jan 03 2019
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EXAMPLE
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The canonical prime factorization of a(3) = 1801800 is 2^3*3^2*5^2*7*11*13. The prime signature of 1801800 is therefore (3,2,2,1,1,1). Note that (3,2,2,1,1,1) contains exactly one number that appears once (3), one number that appears twice (2), and one number that appears three times (1).
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MATHEMATICA
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Table[Product[Times@@Prime[i*(i-1)/2+Ceiling[Range[i*(n-i)]/(n-i)]], {i, n-1}], {n, 6}] (* Gus Wiseman, Jan 03 2019 *)
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PROG
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(PARI) a(n) = if(n == 0, return(1)); my(f = matrix(binomial(n+1, 2), 2)); f[, 1] = primes(#f~ )~; f[, 2] = Vecrev(concat(vector(n, i, vector(n+1-i, j, i))))~; factorback(f) \\ David A. Corneth, Jan 03 2019
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CROSSREFS
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Cf. A006939, A181819, A182855.
Cf. A056239, A059404, A062770, A071625, A118914, A181821, A182857, A323022.
Sequence in context: A231024 A121493 A078491 * A101896 A130411 A262079
Adjacent sequences: A182853 A182854 A182855 * A182857 A182858 A182859
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KEYWORD
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nonn,easy
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AUTHOR
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Matthew Vandermast, Jan 05 2011
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STATUS
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approved
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