The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A245787 Numbers n such that tau(n)*sigma(n) divides n^2. 1
 1, 26208, 56896, 293760, 997920, 9694080, 23569920, 25159680, 29669760, 67858560, 117849600, 132723360, 208565280, 222963840, 276756480, 427714560, 513786240, 578672640, 628992000, 649503360, 688279680, 714954240, 779950080, 830269440, 979102080, 1037266560 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(11) > 10^8. - Derek Orr, Aug 08 2014 Numbers n such that n^2 / (A000005(n) * A000203(n)) is integer. Subsequence of A090777 (numbers n such that sigma(n) divides n^2). Sequence of numbers k(n) = n^2 / (tau(n) * sigma(n)): 1, 104, 889, 612, 945, 7344, … LINKS Jens Kruse Andersen, Table of n, a(n) for n = 1..47 MATHEMATICA a245787[n_Integer] := Select[Range[n], Divisible[#^2, DivisorSigma[0, #]*DivisorSigma[1, #]]&] (* Michael De Vlieger, Aug 09 2014 *) PROG (Magma) [n: n in [1..1000000] | Denominator(n^2 / ((#[d: d in Divisors(n)])* SumOfDivisors(n))) eq 1] (PARI) for(n=1, 10^8, if(n^2%(numdiv(n)*sigma(n))==0, print1(n, ", "))) \\ Derek Orr, Aug 08 2014 CROSSREFS Cf. A000005, A000203, A071707, A090777. Sequence in context: A250972 A235096 A235900 * A034622 A004046 A031652 Adjacent sequences: A245784 A245785 A245786 * A245788 A245789 A245790 KEYWORD nonn AUTHOR Jaroslav Krizek, Aug 08 2014 EXTENSIONS a(7)-a(10) from Derek Orr, Aug 08 2014 a(11)-a(26) from Jens Kruse Andersen, Aug 13 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 22 07:42 EDT 2024. Contains 374481 sequences. (Running on oeis4.)