%I
%S 1,2,20,3,30,31,4,40,41,42,5,50,51,52,53,6,60,61,62,63,64,7,70,71,72,
%T 73,74,75,8,80,81,82,83,84,85,86,9,90,91,92,93,94,95,96,97,10,100,101,
%U 102,103,104,105,106,107,108,11,110,111,112,113,114,115,116,117,118,119,12
%N Triangle in which nth row contains the first n numbers, not already present, that begin with n.
%C Every positive number appears exactly once. Proof: N will appear as the first term of row N, unless it has already appeared. And no term is repeated, by definition.
%C The first term of the 20th row is 200 unlike the 20th row of A077339 where it is 20.
%H M. F. Hasler, <a href="/A077341/b077341.txt">Table of n, a(n) for n = 1..5350</a>
%e Triangle begins:
%e 1
%e 2 20
%e 3 30 31
%e 4 40 41 42
%e 5 50 51 52 53
%e ...
%o (PARI) {u=[];for(m=1,19,o=0;for(n=1,m,while(setsearch(u,a=A077339(m,n+o)),o++);u=setunion(u,Set(a));print1(a",")))} \\ _M. F. Hasler_, Jan 08 2013
%Y Cf. A077339, A077340 (see there for differences), A077342, A077343.
%K base,easy,nonn,tabl
%O 1,2
%A _Amarnath Murthy_, Nov 05 2002
%E Edited by _N. J. A. Sloane_, Jun 12 2007
