This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A145680 #19 Apr 19 2016 01:10:16 %S A145680 6,2,3,4,5,216,7,8,9,5292000,11,10584000,13,4991499040640000,165375, %T A145680 16,17,235270656,19,101867327360000, %U A145680 8107610881081625211441398582431641600000,19235716742537891017605454376709022095843377283072000000,23,552063590295800832,25 %N A145680 a(n) = smallest number m such that UnitarySigma(m) = nm/(n-1). %C A145680 If n=p^i+1 then a(n)=p^i. %C A145680 Unitary sigma = A034448 = sum of divisors d with gcd(d,m/d)=1. %C A145680 Note that a(27) > 10^70. - _Jack Brennen_, Feb 04 2014 %e A145680 UnitarySigma(216) = 2^2*3^2*7 = (7/6)*216. %Y A145680 Cf. A034448. %Y A145680 Related sequences include A145681 (and A144672, A144673, A144674) for 3/2-URPMS, and A144949-A144951 for 5/4-URPMS. - _M. F. Hasler_, Jan 29 2014 %K A145680 nonn %O A145680 2,1 %A A145680 _Yasutoshi Kohmoto_ Mar 09 2009 %E A145680 Corrected a(13) and added a(22) found by _Jack Brennen_. _M. F. Hasler_, Feb 04 2014 %E A145680 a(23)-a(26) from _Jack Brennen_, Feb 04 2014