OFFSET
1,2
COMMENTS
Does every number appear at least once? Do some numbers like 1 appear infinitely often? - Robert G. Wilson v, Oct 10 2001
Difference between n-th triangular number and largest square pyramidal number (A000330) less than it. - Franklin T. Adams-Watters, Sep 11 2006
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = n(n+1)/2 - max_{p(m) < n(n+1)/2} p(m), where p(m) = m(m+1)(2m+1)/6. - Franklin T. Adams-Watters, Sep 11 2006
EXAMPLE
The triangle begins:
....1
...1.2
..3.4.1
.2.3.4.5
6.7.8.9.1
MATHEMATICA
a = {}; Do[a = Append[a, Table[i, {i, 1, n^2} ]], {n, 1, 100} ]; a = Flatten[a]; Do[Print[a[[n(n + 1)/2]]], {n, 1, 100} ]
With[{nn=20}, TakeList[Flatten[Table[Range[n^2], {n, nn}]], Range[Floor[ (Sqrt[8*nn^3+12*nn^2+4*nn+3]/Sqrt[3]-1)/2]]]][[All, -1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 04 2020 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Floor van Lamoen, Oct 08 2001
EXTENSIONS
More terms from Robert G. Wilson v, Oct 10 2001
STATUS
approved