16, 21, 26, 31 and a=16

Question

a=16, what is a0?

Answer 1

a₀=16, a₁=21, a₂=26, a₃=31.

a₁=a₀+5,

a₂=a₁+5=a₀+5+5=a₀+10,

a₃=a₂+5=a₀+10+5=a₀+15.

This is an arithmetic progression or series.

If we take a₃ for example, we can see a₃=a₀+3×5.

The subscript of the a term is also the required multiple of 5, so we can write the general term:

a_n=a₀+5n, so we replace n with any number to find the specific term.

If we need a₁₆, then a₁₆=a₀+16×5=16+80=96. So a₁₆=96.