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 A145680 a(n) = smallest number m such that UnitarySigma(m) = nm/(n-1). 1
 6, 2, 3, 4, 5, 216, 7, 8, 9, 5292000, 11, 10584000, 13, 4991499040640000, 165375, 16, 17, 235270656, 19, 101867327360000, 8107610881081625211441398582431641600000, 19235716742537891017605454376709022095843377283072000000, 23, 552063590295800832, 25 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS If n=p^i+1 then a(n)=p^i. Unitary sigma = A034448 = sum of divisors d with gcd(d,m/d)=1. Note that a(27) > 10^70. - Jack Brennen, Feb 04 2014 LINKS Table of n, a(n) for n=2..26. EXAMPLE UnitarySigma(216) = 2^2*3^2*7 = (7/6)*216. CROSSREFS Cf. A034448. 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 Sequence in context: A093408 A222223 A284821 * A094775 A362922 A019662 Adjacent sequences: A145677 A145678 A145679 * A145681 A145682 A145683 KEYWORD nonn AUTHOR Yasutoshi Kohmoto Mar 09 2009 EXTENSIONS Corrected a(13) and added a(22) found by Jack Brennen. M. F. Hasler, Feb 04 2014 a(23)-a(26) from Jack Brennen, Feb 04 2014 STATUS approved

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Last modified May 20 14:08 EDT 2024. Contains 372717 sequences. (Running on oeis4.)