40+1 39+2 38+3 37+4 36+5 35+6 34+7 33+8 32+9 31+10 30+11 29+12 28+13 27+14 26+15 25+16 24+17 23+18 22+19 21+20 20+21 19+22 18+23 17+24 16+25 15+26 14+27 13+28 12+29 11+30 10+31 9+32 8+33 7+34 6+35 5+36 4+37 3+38 2+39 1+40 These are all operations with natural numbers. More complicated operations look like these: 23,5+17,5 = 41 -1+42 = 41 etc...
... equals an even number
Yes, the sum is always rational.
2+n
70
4507 5267 - 500 - 200 - 60 = 4507