login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A127731 Triangle read by rows, where row n consists of the r's where r = (n*m)/(n+m) and the m's are positive integers such that (n+m) divides (n*m). 1
1, 2, 2, 3, 4, 2, 3, 4, 5, 6, 4, 6, 7, 6, 8, 5, 6, 8, 9, 10, 3, 4, 6, 8, 9, 10, 11, 12, 7, 10, 12, 13, 6, 10, 12, 14, 8, 12, 14, 15, 16, 6, 9, 12, 14, 15, 16, 17, 18, 4, 10, 12, 15, 16, 18, 19, 12, 14, 18, 20, 11, 18, 20, 21, 22, 6, 8, 12, 15, 16, 18, 20, 21, 22, 23, 20, 24, 13, 22, 24, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

The maximum term of the n-th row, for n >= 2, is (n-1). The minimum term of row n is A063428(n), for n >= 3. Row n contains A063647(n) terms (according to a comment by Benoit Cloitre). For p prime, row p^k has k terms. (Each term in row p^k is of the form p^(k-j)*(p^j -1), 1<=j<=k.)

LINKS

Table of n, a(n) for n=2..82.

EXAMPLE

Row 6 is (2,3,4,5) because row 6 of irregular array A127730 is (3,6,12,30); and (6*3)/(6+3) = 2, (6*6)/(6+6) = 3, (6*12)/(6+12) = 4 and (6*30)/(6+30) = 5.

MATHEMATICA

f[n_] := Select[Table[n*m/(n + m), {m, n^2}], IntegerQ]; Table[f[n], {n, 2, 26}] // Flatten(*Chandler*)

CROSSREFS

Cf. A063428, A063647, A127730.

Sequence in context: A187200 A117632 A236241 * A159978 A230546 A286617

Adjacent sequences:  A127728 A127729 A127730 * A127732 A127733 A127734

KEYWORD

nonn,tabf

AUTHOR

Leroy Quet, Jan 26 2007

EXTENSIONS

Extended by Ray Chandler, Feb 13 2007

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 24 14:36 EDT 2019. Contains 326285 sequences. (Running on oeis4.)