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A126287 a(1) = 1, a(2) = 1, a(n) = n * LeastPrimeFactor(n-1) / LeastPrimeFactor(n).

%I A126287 #12 Jun 02 2025 00:31:36
%S A126287 1,1,2,6,2,15,2,28,6,15,2,66,2,91,10,24,2,153,2,190,14,33,2,276,10,65,
%T A126287 18,42,2,435,2,496,22,51,14,90,2,703,26,60,2,861,2,946,30,69,2,1128,
%U A126287 14,175,34,78,2,1431,22,140,38,87,2,1770,2,1891,42,96,26,165,2,2278,46,105
%N A126287 a(1) = 1, a(2) = 1, a(n) = n * LeastPrimeFactor(n-1) / LeastPrimeFactor(n).
%H A126287 Ivan Neretin, <a href="/A126287/b126287.txt">Table of n, a(n) for n = 1..10000</a>
%F A126287 a(n) = A032742(n)*A020639(n-1), for n>2. - _Michel Marcus_, May 20 2015
%e A126287 a(6) = 6 * LeastPrimeFactor(5) / LeastPrimeFactor(6) = 6 * 5 / 2 = 15
%p A126287 N:= 1000: # to get a(1) to a(n)
%p A126287 a[1]:= 1: a[2]:= 1:
%p A126287 b:= 2:
%p A126287 for n from 3 to N do
%p A126287 c:= min(numtheory:-factorset(n));
%p A126287 a[n]:= n*b/c;
%p A126287 b:= c;
%p A126287 od:
%p A126287 seq(a[n],n=1..N); # _Robert Israel_, May 20 2015
%t A126287 a[1] := 1; a[2] := 1; a[n_] := n*FactorInteger[n - 1][[1, 1]]/FactorInteger[n][[1, 1]]; Table[a[n], {n, 70}] (* _Ivan Neretin_, May 20 2015 *)
%Y A126287 Cf. A126286, A126288, A126289, A020639.
%K A126287 easy,nonn
%O A126287 1,3
%A A126287 _Lior Manor_, Dec 25 2006