OFFSET
0,3
COMMENTS
m^2 (when n is m-th triangular number) followed by m copies of m-th pronic [m(m+1)].
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
FORMULA
EXAMPLE
a(9) = 12 since spiral is as marked by 9 X's in 4*3 = 12 rectangle:
X.XX
X..X
XXXX
MATHEMATICA
ar[n_]:=Module[{c=(Sqrt[8n+1]-1)/2}, Floor[c]Ceiling[c]]; Array[ar, 70, 0] (* Harvey P. Dale, Feb 27 2012 *)
PROG
(Haskell)
a056942 n = a056942_list !! n
a056942_list = concatMap
(\x -> (x ^ 2) : (take x $ repeat (x * (x + 1)))) [0..]
-- Reinhard Zumkeller, Feb 11 2014
CROSSREFS
KEYWORD
easy,nice,nonn
AUTHOR
Henry Bottomley, Jul 13 2000
STATUS
approved