A167232 a(n) is the number obtained by writing out numbers from 1 to n and placing an alternate + and - minus sign between successive digits and evaluating the expression written.

1, -1, 2, -2, 3, -3, 4, -4, 5, 4, 4, 3, 4, 3, 5, 4, 7, 6, 10, 9, 14, 13, 19, 18, 25, 24, 32, 31, 40, 38, 38, 36, 37, 35, 37, 35, 38, 36, 40, 38, 43, 41, 47, 45, 52, 50, 58, 56, 65, 62, 62, 59, 60, 57, 59, 56, 59, 56, 60, 57, 62, 59, 65, 62, 69, 66, 74, 71, 80, 76, 76, 72, 73, 69

Offset: 1

Author

Dhruv (dhruvbird(AT)gmail.com), Oct 31 2009

Keywords

• sign
• base

Links

• Sphere Online Judge, Problem 1433: The Sum

Crossrefs

Cf. A007376.

Formula

a(n) = -Sum_{i=1..n} (-1)^i*A007376(i). [R. J. Mathar, Nov 09 2009]

Extensions

a(12) corrected, more terms appended by R. J. Mathar, Nov 09 2009