login
A093496
Least k such that for every 1 < r < n there exists a distinct s, n < s <= k so that r and s have the same prime signature.
3
5, 7, 11, 13, 17, 19, 27, 49, 49, 49, 49, 49, 49, 49, 81, 81, 81, 81, 81, 81, 81, 81, 121, 169, 169, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 343, 361, 361, 361, 361, 361, 361, 361, 361, 361, 361
OFFSET
3,1
LINKS
EXAMPLE
a(9) = 27. For r = 2,3,4,5,6,7,8 the corresponding s values are 11,13,25,17,10,19 and 27.
From Michael De Vlieger, Nov 26 2017: (Start)
First position n of unique values:
a(n) n
------------
5 3
7 4
11 5
13 6
17 7
19 8
27 9
49 10
81 17
121 25
169 26
343 28
361 50
729 65
2401 82
3125 243
16807 244
(End)
MATHEMATICA
With[{s = Values@ PositionIndex@ Array[Sort[FactorInteger[#][[All, -1]], Greater] &, 10^4]}, Table[Max@ Fold[Function[{t, k}, Append[t, SelectFirst[DeleteCases[s[[FirstPosition[s, k][[1]] ]], _?(# <= n &) ], FreeQ[t, #] &]]], {}, Range[2, n - 1]], {n, 3, 60}] ] (* Michael De Vlieger, Nov 26 2017 *)
CROSSREFS
Sequence in context: A346676 A309726 A093495 * A171688 A239711 A217090
KEYWORD
less,nonn
AUTHOR
Amarnath Murthy, Apr 16 2004
EXTENSIONS
More terms from David Wasserman, Oct 16 2006
STATUS
approved