|
Search: id:A123396
|
|
|
| A123396 |
|
a(n) = number of earlier terms each of which, when added to n, give a triangular number. |
|
+0
2
|
|
| 0, 1, 1, 1, 0, 3, 2, 1, 1, 5, 3, 0, 2, 2, 5, 3, 2, 0, 3, 4, 5, 4, 0, 3, 2, 5, 5, 5, 5, 0, 0, 7, 2, 5, 6, 5, 7, 0, 2, 1, 9, 2, 5, 8, 6, 8, 1, 2, 2, 2, 10, 2, 5, 12, 8, 8, 1, 1, 4, 2, 2, 11, 3, 6, 14, 9, 9, 1, 1, 3, 4, 2, 3, 11, 4, 8, 15, 12, 8, 2, 2, 1, 3, 6, 2, 4, 11, 6, 9, 18, 13, 9, 1, 2, 3, 1, 5, 6, 2, 6
(list; graph; listen)
|
|
|
OFFSET
|
0,6
|
|
|
LINKS
|
Leroy Quet, Home Page (listed in lieu of email address)
|
|
EXAMPLE
|
a(0)+10 = 10, a(1)+10 = 11, a(2)+10 = 11, a(3)+10 = 11, a(4)+10 = 10, a(5)+10 = 13, a(6)+10 = 12, a(7)+10 = 11, a(8)+10 = 11 and a(9)+10 = 15. Of these, three terms (a(0), a(4), a(9)) are such that, when each is added to 10, the result is a triangular number (i.e. of the form m(m+1)/2). Hence a(10) = 3.
|
|
MATHEMATICA
|
f[l_List] := Append[l, Length[Select[l + Length[l], IntegerQ[Sqrt[8# + 1]] &]]]; Nest[f, {0}, 100] (*Chandler*)
|
|
PROGRAM
|
(PARI) {m=100; v=vector(m+1); print1(v[1]=0, ", "); for(n=1, m, c=0; for(k=1, n, a=n+v[k]; b=sqrtint(2*a); if(b*(b+1)/2==a, c++)); print1(v[n+1]=c, ", "))} - (Klaus Brockhaus, Oct 16 2006)
|
|
CROSSREFS
|
Cf. A000217.
Sequence in context: A097794 A137683 A046225 this_sequence A058280 A113185 A132069
Adjacent sequences: A123393 A123394 A123395 this_sequence A123397 A123398 A123399
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Leroy Quet Oct 14 2006
|
|
EXTENSIONS
|
More terms from Ray Chandler (rayjchandler(AT)sbcglobal.net) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Oct 16 2006
|
|
|
Search completed in 0.002 seconds
|
