a binomial sum.

[Ralf Stephan]

> I was about to submit the following signed sequence (offset 0),
> 
> 1, -1, 7, -21, 81, -295, 1107, -4165, 15793, -60171, 230253, -884235, 3406105, -13154947, 50922987, -197519941, 767502945, -2987013067, 11641557717, -45429853651, 177490745985, ...,

Check A072547, the members are the absolute values of your sequence
differing only by -1, +1, -1, +1, -1. Not easy to find. 


in a hurry,
ralf