cp's OEIS Frontend

A318701 Tetrahedral numbers that are not divisible by any smaller tetrahedral number except 1.

%I A318701 #37 Dec 28 2018 13:32:04
%S A318701 1,4,10,35,165,286,969,1771,2925,3654,4495,9139,12341,16215,23426,
%T A318701 32509,39711,47905,52394,67525,79079,91881,105995,129766,138415,
%U A318701 156849,176851,209934,221815,246905,273819,302621,366145,383306,437989,477191,540274,562475,657359,708561,762355,848046,939929,1004731
%N A318701 Tetrahedral numbers that are not divisible by any smaller tetrahedral number except 1.
%H A318701 Robert Israel, <a href="/A318701/b318701.txt">Table of n, a(n) for n = 1..10000</a>
%e A318701 4 is a term because it is divisible by 1.
%e A318701 10 is a term because it is divisible by 1 but not by 4.
%p A318701 count:= 1: Res:= NULL:
%p A318701 for i from 2 while count < 100 do
%p A318701   r:= i*(i+1)*(i+2)/6;
%p A318701   if not ormap(t -> (r/t)::integer,[Res]) then
%p A318701     Res:= Res, r;
%p A318701     count:= count+1;
%p A318701   fi
%p A318701 od:
%p A318701 1,Res; # _Robert Israel_, Dec 28 2018
%t A318701 t[n_]:=n(n+1)(n+2)/6; tQ[n_] := Module[{ans=True, tn=t[n]}, Do[If[Divisible[tn,t[i]], ans=False; Break[]],{i,2,n-1}]; ans]; t[Select[Range[100], tQ]] (* _Amiram Eldar_, Nov 14 2018 *)
%o A318701 (PARI) t(n) = n*(n+1)*(n+2)/6;
%o A318701 isok(n) = my(tn=t(n)); for(i=2, n-1, if (!(tn % t(i)), return (0))); return (1);
%o A318701 lista(nn) = for (n=1, nn, if (isok(n), print1(t(n), ", "))); \\ _Michel Marcus_, Sep 29 2018
%Y A318701 Cf. A000292, A319788.
%K A318701 nonn
%O A318701 1,2
%A A318701 _Torlach Rush_, Aug 31 2018
%E A318701 a(1) = 1 inserted by _Michel Marcus_, Nov 09 2018