login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 A019662 A330531

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 8 11:31 EDT 2020. Contains 336298 sequences. (Running on oeis4.)