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A081880 Triangle read by rows: n-th row gives trajectory of 2n under the map x->(x^2-4)/6, stopping when the next term would be negative or nonintegral.

%I A081880 #7 Jul 01 2025 19:22:51
%S A081880 0,2,0,4,2,0,6,8,10,16,42,10,16,42,12,14,32,170,4816,3865642,
%T A081880 2490531345360,16,42,18,20,66,22,80,1066,189392,5978221610,
%U A081880 5956522269711832016,5913359591595499145281505571167104042,5827970276585748074286667660065476529979312208145367609757859954142122960,24,26
%N A081880 Triangle read by rows: n-th row gives trajectory of 2n under the map x->(x^2-4)/6, stopping when the next term would be negative or nonintegral.
%H A081880 Pierre Abbat, <a href="http://phma.optus.nu/Math/64-100.html">The 64-100 Sequences</a>
%e A081880 8 -> (64-4)/6 = 10 -> (100-4)/6 = 16 -> (256-4)/6 = 42 -> (42^2-4)/6 nonintegral, so stop; thus row 4 is (8, 10, 16, 42).
%e A081880 Triangle begins:
%e A081880 0,
%e A081880 2, 0,
%e A081880 4, 2, 0,
%e A081880 6,
%e A081880 8,
%e A081880 10, 16, 42, 10, 16, 42,
%e A081880 12,
%e A081880 14, 32, 170, 4816, 3865642, 2490531345360,
%e A081880 16, 42,
%e A081880 18,
%e A081880 20, 66,
%e A081880 22, 80, 1066, 189392, 5978221610, 5956522269711832016, 5913359591595499145281505571167104042, 5827970276585748074286667660065476529979312208145367609757859954142122960,
%e A081880 24,
%e A081880 ...
%K A081880 nonn,tabf
%O A081880 0,2
%A A081880 _Pierre Abbat_, Apr 12 2003