> gap> [1,3..16]; > Error, Range: <last>-<first> (15) must be divisible by <inc> (2) > not in any function at line 1 of *stdin* > (why <last>-<first> must be divisible by <inc> in GAP is another > good question). because when in a math book I see 1+3+...+n and n=9 I think it means 1+3+5+7+9, when n=8 I think there is an error somewhere