Oh, dude, like, the concept of numbers has been around for ages, you know? But if you're talking about the specific sequence 123456789, I mean, that's just a natural progression of numbers, man. It's like asking who invented counting - it's been around forever, like before the dinosaurs or something.
123456789 + 123456789 = 246913578
the answer is 15241578750190521
you get cheese
15,241,578,750,190,521
324536
543234567890-123456789 = 543111111101
1
123456789 +987654321 =1111111110
123456789-987654321 = -864197532
1.524157875019052e+16
1234567 + 123456789 = 124691356
123456789*1