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

1,2

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A079809.

Sequence in context: A225907 A107020 A160945 * A089658 A219100 A140322

Adjacent sequences: A079805 A079806 A079807 * A079809 A079810 A079811

Keyword

base,nonn

Author

Amarnath Murthy, Feb 10 2003

Status

approved