Have a look at this one!

$1,2,4,7,12,\dots,\boxed{a_{10}=?},\dots$ The above sequence has Fibonacci-type behavior such that; $a_1=1,a_2=2\, and \, a_n=a_{n-1}+a_{n-2}+1 \, where \, n \ge 3$ Hence we have the sequence as:

• $a_{1}=1$

• $a_{2}=2$

• $a_{3}=4$

• $a_{4}=7$

• $a_{5}=12$

• $a_{6}=20$

• $a_{7}=33$

• $a_{8}=54$

• $a_{9}=88$

• $a_{10}=\boxed{143}$

Hence $\boxed{a_{10}-1=142}$ :)