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

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A177028 Irregular table: row n contains values k (in descending order) for which n is a k-gonal number. 2
3, 4, 5, 6, 3, 7, 8, 9, 4, 10, 3, 11, 12, 5, 13, 14, 15, 6, 3, 16, 4, 17, 18, 7, 19, 20, 21, 8, 3, 22, 5, 23, 24, 9, 25, 4, 26, 27, 10, 28, 6, 3, 29, 30, 11, 31, 32, 33, 12, 34, 7, 35, 5, 36, 13, 4, 3, 37, 38, 39, 14, 40, 8, 41, 42, 15 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Every row begins with n and contains all values of k for which n is a k-gonal number.

The cardinality of row n is A177025(n). In particular, if n is prime, then row n contains only n.

LINKS

T. D. Noe, Rows n = 3..1000, flattened

EXAMPLE

The table starts with row n=3 as:

3;

4;

5;

6, 3;

7;

8;

9, 4;

10, 3;

11;

12, 5;

13;

14;

15, 6, 3;

16, 4;

17;

18, 7;

19;

20;

Before n=37, we have row n=36: {36, 13, 4, 3}. Thus 36 is k-gonal for k=3, 4, 13 and 36.

MAPLE

P := proc(n, k) n/2*((k-2)*n-k+4) ; end proc:

A177028 := proc(n) local k , j, r, kg ; r := {} ; for k from n to 3 by -1 do for j from 1 do kg := P(j, k) ; if kg = n then r := r union {k} ; elif kg > n then break ; end if; end do; end do: sort(convert(r, list), `>`) ; end proc:

for n from 3 to 20 do print(A177028(n)) ; end do: # R. J. Mathar, Apr 17 2011

MATHEMATICA

nn = 100; t = Table[{}, {nn}]; Do[n = 2; While[p = n*(4 - 2*n - r + n*r)/2; p <= nn, AppendTo[t[[p]], r]; n++], {r, 3, nn}]; Flatten[Reverse /@ t] (* T. D. Noe, Apr 18 2011 *)

CROSSREFS

Cf. A139600, A177025, A176948, A176774, A176775.

Sequence in context: A004484 A176210 A187824 * A162552 A133575 A230113

Adjacent sequences:  A177025 A177026 A177027 * A177029 A177030 A177031

KEYWORD

nonn,tabf

AUTHOR

Vladimir Shevelev, May 01 2010

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.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 5 09:15 EST 2016. Contains 278762 sequences.