Question Number 141693 by Fikret last updated on 22/May/21
$${n}\in{N}^{+} \\ $$$${a}_{\mathrm{5}} ={a}_{\mathrm{13}} =\mathrm{0} \\ $$$${b}_{{n}+\mathrm{1}} −{b}_{{n}} =\mathrm{2} \\ $$$${b}_{{n}} ={a}_{{n}+\mathrm{1}} −{a}_{{n}} \:\:\:\Rightarrow\:\:{a}_{\mathrm{1}} =? \\ $$$$ \\ $$