A124751 Expansion of (1+x^2+x^4)/(1-x^6+x^7).

1, 0, 1, 0, 1, 0, 1, -1, 1, -1, 1, -1, 1, -2, 2, -2, 2, -2, 2, -3, 4, -4, 4, -4, 4, -5, 7, -8, 8, -8, 8, -9, 12, -15, 16, -16, 16, -17, 21, -27, 31, -32, 32, -33, 38, -48, 58, -63, 64, -65, 71, -86, 106, -121, 127, -129, 136, -157, 192, -227, 248

Offset: 0

Author

Paul Barry, Nov 06 2006

Keywords

• easy
• sign

Comments

Diagonal sums of number triangle A124749.

Links

• Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,1,-1).

Programs

Mathematica

CoefficientList[Series[(1+x^2+x^4)/(1-x^6+x^7),{x,0,100}],x] (* or *) LinearRecurrence[{0,0,0,0,0,1,-1},{1,0,1,0,1,0,1},100] (* Harvey P. Dale, Mar 10 2017 *)

Formula

a(n)=sum{k=0..floor(n/2), C(floor(k/3),n-2k)*(-1)^n}