This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A145551 Numbers n such that product of divisors of n / sum of divisors of n is an integer. 6
 1, 6, 28, 30, 66, 84, 102, 120, 210, 270, 318, 330, 364, 420, 462, 496, 510, 546, 570, 642, 672, 690, 714, 840, 868, 870, 924, 930, 966, 1080, 1092, 1122, 1320, 1410, 1428, 1488, 1518, 1590, 1638, 1722, 1770, 1782, 1890, 1932, 2040, 2130, 2226, 2280, 2310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that A007955(n)/A000203(n) is an integer Numbers such that n^sigma_0(n) is a multiple of sigma_1(n)^2. - Chai Wah Wu, Mar 09 2016 REFERENCES Zhang Wengpeng : On the divisor products and proper divisor products sequences,Smarandache Notions Journal,Volume 13, Issue 1-2-3(Spring 2002),pp. 128 - 133, ISSN:1084-2810 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..1100 MAPLE A007955 := proc(n) local dvs, d ; dvs := numtheory[divisors](n) ; mul(d, d=dvs) ; end: A000203 := proc(n) local dvs, d ; dvs := numtheory[divisors](n) ; add(d, d=dvs) ; end: isA145551 := proc(n) RETURN(A007955(n) mod A000203(n) = 0) ; end: for n from 1 to 10000 do if isA145551(n) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Oct 14 2008 MATHEMATICA spQ[n_]:=Module[{ds=Divisors[n]}, IntegerQ[(Times@@ds)/Total[ds]]]; Select[ Range[2500], spQ] (* Harvey P. Dale, Jun 26 2012 *) PROG (Python) from sympy import divisor_sigma A145551_list = [n for n in range(1, 10**3) if not n**divisor_sigma(n, 0) % divisor_sigma(n, 1)**2] # Chai Wah Wu, Mar 09 2016 CROSSREFS Cf. A000203, A007955, A140480 Sequence in context: A211679 A261868 A105402 * A259917 A083865 A185351 Adjacent sequences:  A145548 A145549 A145550 * A145552 A145553 A145554 KEYWORD easy,nonn AUTHOR Ctibor O. Zizka, Oct 13 2008 EXTENSIONS 90, 96, 108, 126, 132, 140 removed, extended by R. J. Mathar, Oct 14 2008 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 15 05:56 EDT 2018. Contains 316202 sequences. (Running on oeis4.)