|
Search: id:A161943
|
|
|
| A161943 |
|
a(n) is the number of different equalities that can be made by summing numbers from 1 to n and using every number not more than once. |
|
+0
3
|
|
| 0, 0, 1, 3, 7, 17, 43, 108, 273, 708, 1867, 4955, 13256, 35790, 97340, 266240, 732014, 2022558, 5612579, 15634288, 43702232, 122550885, 344661924, 971908613, 2747404212, 7784038617, 22100387619, 62869809733, 179173559128
(list; graph; listen)
|
|
|
OFFSET
|
1,4
|
|
|
EXAMPLE
|
a(3) = 1, as the only equality we can make by summing numbers from the set 1, 2, and 3 is 1+2 = 3. a(4) = 3, as we can make three equalities: 1+2=3, 1+3=4, 1+4=2+3.
|
|
MAPLE
|
b:= proc(n, m, i) option remember; if n<0 or m<0 then 0 elif n=0 and m=0 then 1 elif i<1 then 0 elif m<n then b(m, n, i) else b(n, m, i-1) +b(n-i, m, i-1) +b(n, m-i, i-1) fi end: a:= n-> add (b (k, k, n), k=3..floor (n*(n+1) /4)) /2: seq (a(n), n=1..30); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 31 2009]
|
|
MATHEMATICA
|
Table[(Length[ Select[Range[0, 3^n - 1], Apply[Plus, Pick[Range[n], PadLeft[IntegerDigits[ #, 3], n], 1]] == Apply[Plus, Pick[Range[n], PadLeft[IntegerDigits[ #, 3], n], 2]] &]] - 1)/ 2, {n, 14}]
|
|
CROSSREFS
|
Sequence in context: A020730 A003440 A102071 this_sequence A134184 A142975 A114589
Adjacent sequences: A161940 A161941 A161942 this_sequence A161944 A161945 A161946
|
|
KEYWORD
|
nonn,uned
|
|
AUTHOR
|
Tanya Khovanova (tanyakh(AT)yahoo.com), Jun 22 2009
|
|
EXTENSIONS
|
More terms from Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 31 2009
|
|
|
Search completed in 0.002 seconds
|
