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.

1, 2, 11, 42, 133, 622, 1531, 8244, 17335, 102642, 193551, 1228446, 11137537, 142104662, 113395571, 1621248648, 11531157739, 182144106682, 117313597591, 20216412688410, 119315511779311, 2221841461086102, 1213175137995111

Offset: 1

Author

Amarnath Murthy, Feb 10 2003

Keywords

• base
• nonn

Examples

			Triangle begins as:
  1;
  2 1;
  1 2 3;
  4 3 2 1;
  1 2 3 4 5;
  6 5 4 3 2 1;
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..650

Crossrefs

Cf. A079809.

Programs

Mathematica

a[n_] := FromDigits[Join@@Table[IntegerDigits[If[EvenQ[n+1-i], n+2-2i, i]], {i, 1, Ceiling[n/2]}]]