No, such integers do not exist. This shall be proven by contradiction, by showing that if a5b+3 is a perfect cube then ab5+3 cannot be.
Remark that perfect cubes are always congruent to 0 , 1 , or −1 modulo 9 . Therefore, if a5b+3≡0,1, or−1(mod9) , then a5b≡5,6, or 7(mod9) .
If a5b≡6(mod9) , then note that 3∣b . (This is because if 3∣a then a5b≡0(mod9) .) Therefore ab5≡0(mod9) and ab5+3≡3(mod9) , contradiction.
Otherwise, either a5b≡5(mod9) or a5b≡7(mod9) . Note that since a6b6 is a perfect sixth power, and since neither a nor b contains a factor of 3 , a6b6≡1(mod9) . If a5b≡5(mod9) , then a6b6≡(a5b)(ab5)≡5ab5≡1(mod9)⟹ab5≡2(mod9). Similarly, if a5b≡7(mod9) , then a6b6≡(a5b)(ab5)≡7ab5≡1(mod9)⟹ab5≡4(mod9). Therefore ab5+3≡5,7(mod9) , contradiction.
Therefore no such integers exist.
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