Calculation with recurrence equation -- ① 1 + 2 +... + 19 + 21 ② 2 + 4 +... + 68 + 70

Calculation with recurrence equation -- ① 1 + 2 +... + 19 + 21 ② 2 + 4 +... + 68 + 70

Recursive equation calculation?
It is the sum of the first n terms of two arithmetic sequences
①1+2+...+19+21=（1+21）*21/2=231；
②2+4+...+68+70=（2+70)*35/2=1260.
PS: the formula used is: (first item + last item) * number of items / 2

18000-302 × 19 recursive equation calculation
1 urgent

18000-302×19
=18000-302×（20-1）
=18000-6040+302
=11960+302
=12262

4 5 8 10 11 16 19 32 36 which is redundant

11 is a redundant number
The sequence should be: 4, 5, 8, 10, 16, 19, 32, 36
The rule is: odd term an: 2 ^ (K + 1) (n = 2K + 1)
Even term: an = a (n-1) + n / 2