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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A138808 Number of integer pairs (x,y), x > 0, y > 0, such that x <= p, y <= q for any factorization n = p*q. 2
 1, 3, 5, 8, 9, 14, 13, 20, 21, 26, 21, 35, 25, 38, 41, 48, 33, 57, 37, 64, 61, 62, 45, 84, 65, 74, 81, 96, 57, 109, 61, 112, 101, 98, 101, 138, 73, 110, 121, 151, 81, 160, 85, 160, 161, 134, 93, 196, 133, 185, 161, 192, 105, 216, 173, 223, 181, 170, 117, 258 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Conjecture: the row sums of the plane partitions A010766 are upper bounds. - R. J. Mathar, Aug 06 2008 a(n) is divisible by n iff n=1 or n belongs to A227993. - Rémy Sigrist, Mar 06 2017 a(n) >= 2*n - 1, with equality iff n is not composite. - Rémy Sigrist, Mar 12 2017 LINKS Paul Tek, Table of n, a(n) for n = 1..10000 Rémy Sigrist, Illustration of the first terms FORMULA a(n) = n*(m - Sum_{k=1..m-1} d(k)/d(k+1)), where d(1) < d(2) < ... < d(m) denote the divisors of n. - Rémy Sigrist, Mar 06 2017 EXAMPLE a(8) = these 20 marked *'s: -|12345678 -+-------- 1|******** 2|**** 3|** 4|** 5|* 6|* 7|* 8|* PROG (PARI) a(n) = my(ar=0, pw=0); fordiv(n, w, ar=ar+(w-pw)*n/w; pw=w); return (ar) \\ Paul Tek, Mar 21 2015 CROSSREFS Cf. A227993. Sequence in context: A002159 A050094 A137319 * A185456 A308405 A331314 Adjacent sequences:  A138805 A138806 A138807 * A138809 A138810 A138811 KEYWORD nonn AUTHOR Jonas Wallgren, May 16 2008 EXTENSIONS More terms from Paul Tek, Mar 21 2015 Typo in name corrected by Rémy Sigrist, Mar 05 2017 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 May 18 12:03 EDT 2022. Contains 353807 sequences. (Running on oeis4.)