Search: id:A067270
Results 1-1 of 1 results found.

%I A067270
%S A067270 1,5,25,625,9376,90625,890625,7109376,12890625,212890625,1787109376,
%T A067270 81787109376,59918212890625,259918212890625,3740081787109376,
%U A067270 56259918212890625,256259918212890625,7743740081787109376
%N A067270 Numbers n such that n-th triangular number (A000217) ends in n.
%C A067270 T_n = n(n+1)/2. Thanks to David W. Wilson for the proof that this sequence 
               is a proper subset of A003226.
%e A067270 T_5 = 15 ends in 5, hence 5 is a term of the sequence.
%t A067270 a5=A018247 less the commas; a6=A018248 less the commas; b5 = FromDigits[ 
               Reverse[ IntegerDigits[a5]]]; b6 = FromDigits[ Reverse[ IntegerDigits[a6]]]; 
               f[0] = 1; f[n_] := Block[{c5 = Mod[b5, 10^n], c6 = Mod[b6, 10^n]}, 
               If[ Mod[c5(c5 + 1)/2, 10^n] == c5, c5, c6]]; Union[ Table[ f[n], 
               {n, 0, 20}]]
%Y A067270 Proper subset of A003226. Cf. A007185, A018247, A016090, A018248.
%Y A067270 Sequence in context: A078260 A007185 A030995 this_sequence A137114 A067212 
               A061583
%Y A067270 Adjacent sequences: A067267 A067268 A067269 this_sequence A067271 A067272 
               A067273
%K A067270 base,nonn
%O A067270 1,2
%A A067270 Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 21 2002
%E A067270 Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 20 
               2002

Search completed in 0.188 seconds