The formula for the nth term of the sequence 1, 5, 14, 30, 55, 91,... is n(n+1)(2n+1)/6 fins the 20th term
the nth term of the sequence 10, 17, 26, 37, 50,... is (n+2)^2 +1
write down the formula for the nth term of the sequence 17, 26, 37, 50, 65,...