cp's OEIS Frontend

A355860 Triangle read by rows: T(n,k) = n*k/(n + k) if n+k divides n*k, otherwise T(n,k) = 0; n >= 1, k >= 1.

%I A355860 #20 Jan 16 2025 14:17:16
%S A355860 0,0,1,0,0,0,0,0,0,2,0,0,0,0,0,0,0,2,0,0,3,0,0,0,0,0,0,0,0,0,0,0,0,0,
%T A355860 0,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,5,0,0,0,0,0,0,0,0,0,0,0,0,0,
%U A355860 0,3,0,4,0,0,0,0,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,7
%N A355860 Triangle read by rows: T(n,k) = n*k/(n + k) if n+k divides n*k, otherwise T(n,k) = 0; n >= 1, k >= 1.
%H A355860 Antti Karttunen, <a href="/A355860/b355860.txt">Table of n, a(n) for n = 1..22155; the first 210 rows of the triangle</a>
%e A355860 The triangle begins:
%e A355860   0;
%e A355860   0, 1;
%e A355860   0, 0, 0;
%e A355860   0, 0, 0, 2;
%e A355860   0, 0, 0, 0, 0;
%e A355860   0, 0, 2, 0, 0, 3;
%e A355860 and so on.
%t A355860 T[n_, k_] := If[Divisible[n*k, n + k], n*k/(n + k), 0]; Table[T[n, k], {n, 1, 12}, {k, 1, n}] // Flatten (* _Amiram Eldar_, Jul 20 2022 *)
%o A355860 (PARI)
%o A355860 up_to = 105;
%o A355860 A355860tr(n,k) = ((q->if(1==denominator(q),q,0))((n*k)/(n+k)));
%o A355860 A355860list(up_to) = { my(v = vector(up_to), i=0); for(n=1,oo, for(k=1,n, if(i++ > up_to, return(v)); v[i] = A355860tr(n,k))); (v); };
%o A355860 v355860 = A355860list(up_to);
%o A355860 A355860(n) = v355860[n]; \\ _Antti Karttunen_, Jan 16 2025
%Y A355860 Cf. also A106448.
%K A355860 nonn,tabl
%O A355860 1,10
%A A355860 _Ctibor O. Zizka_, Jul 19 2022
%E A355860 Data section extended up to a(105) by _Antti Karttunen_, Jan 16 2025