OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..500
EXAMPLE
a(1) through a(4) have prime signatures 0, 1, (1, 1) and 2. a(5) = 20 because 5 has prime signature 1, which has already been used and 10 and 15 have prime signature (1, 1), which has already been used, but 20 has prime signature (2, 1), which has not yet been used.
MATHEMATICA
lps[n_] := Module[{e = ReverseSort[FactorInteger[n][[;; , 2]]]}, Times @@ (Prime[Range[Length[e]]]^e)]; lps[1] = 1; seq[nmax_] := Module[{v = {}, s = Table[0, {nmax}], k}, Do[k = n; While[MemberQ[v, lps[k]], k += n]; AppendTo[v, lps[k]]; s[[n]] = k, {n, 1, nmax}]; s]; seq[50] (* Amiram Eldar, Jul 27 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Apr 25 2002
EXTENSIONS
More terms from David Wasserman, Apr 30 2003
STATUS
approved