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A079808 Consider a triangle in which the 2n-th row contains first 2n positive integers in decreasing order and the (2n+1)-st row contains first 2n+1 positive integers in increasing order; sequence contains concatenation of numbers read upward at a 45-degree angle.

%I A079808 #11 Dec 14 2023 15:40:26
%S A079808 1,2,11,42,133,622,1531,8244,17335,102642,193551,1228446,11137537,
%T A079808 142104662,113395571,1621248648,11531157739,182144106682,117313597591,
%U A079808 20216412688410,119315511779311,2221841461086102,1213175137995111
%N A079808 Consider a triangle in which the 2n-th row contains first 2n positive integers in decreasing order and the (2n+1)-st row contains first 2n+1 positive integers in increasing order; sequence contains concatenation of numbers read upward at a 45-degree angle.
%H A079808 G. C. Greubel, <a href="/A079808/b079808.txt">Table of n, a(n) for n = 1..650</a>
%e A079808 Triangle begins as:
%e A079808   1;
%e A079808   2 1;
%e A079808   1 2 3;
%e A079808   4 3 2 1;
%e A079808   1 2 3 4 5;
%e A079808   6 5 4 3 2 1;
%t A079808 a[n_] := FromDigits[Join@@Table[IntegerDigits[If[EvenQ[n+1-i], n+2-2i, i]], {i, 1, Ceiling[n/2]}]]
%Y A079808 Cf. A079809.
%K A079808 base,nonn
%O A079808 1,2
%A A079808 _Amarnath Murthy_, Feb 10 2003