1 * 1 / 4 + 4 * 1 / 7 + 7 * 1 / 10 + 10 * 1 / 13 + 13 * 1 / 16 + 16 * 1 / 19 + 19 * 1 / 22?

1 * 1 / 4 + 4 * 1 / 7 + 7 * 1 / 10 + 10 * 1 / 13 + 13 * 1 / 16 + 16 * 1 / 19 + 19 * 1 / 22?

an=(3n-2)/(3n+1)=1+3/(3n+1)