cp's OEIS Frontend

A077172 Triangle formed by grouping the natural numbers so that the n-th row contains n numbers whose product has exactly n distinct prime divisors.

%I A077172 #9 May 08 2025 23:48:23
%S A077172 2,1,6,3,4,5,7,8,9,10,11,12,13,14,16,15,17,18,19,20,21,22,23,24,25,26,
%T A077172 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,45,48,44,46,47,49,
%U A077172 50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72
%N A077172 Triangle formed by grouping the natural numbers so that the n-th row contains n numbers whose product has exactly n distinct prime divisors.
%C A077172 Next available unused natural number is added to n-th row unless it would cause product for that row to exceed n prime divisors.
%e A077172 2;
%e A077172 1,6;
%e A077172 3,4,5;
%e A077172 7,8,9,10;
%e A077172 11,12,13,14,16;
%e A077172 15,17,18,19,20,21;
%e A077172 ...
%Y A077172 Cf. A077173, A077174, A077175, A077176, A100918.
%K A077172 nonn,tabl
%O A077172 1,1
%A A077172 _Amarnath Murthy_, Nov 01 2002
%E A077172 Extended by _Ray Chandler_, Nov 29 2004