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%I #21 Feb 02 2023 15:03:31
%S 0,0,0,0,1,1,1,2,4,4,4,6,9,9,9,12,16,16,16,20,25,25,25,30,36,36,36,42,
%T 49,49,49,56,64,64,64,72,81,81,81,90,100,100,100,110,121,121,121,132,
%U 144,144,144,156,169,169,169,182,196,196,196,210,225,225,225,240,256,256,256,272,289,289,289,306
%N a(n) = floor(n/4)*floor((n+1)/4).
%C Oblong numbers, squares and quarter-squares are subsequences: a(A004767(n))=A002378(N); a(A008586(n))=A000290(n); a(A005408(n))=A002620(n). [_Reinhard Zumkeller_, Oct 09 2011]
%H Reinhard Zumkeller, <a href="/A008217/b008217.txt">Table of n, a(n) for n = 0..10000</a>
%F Empirical g.f.: -x^4*(x^2-x+1) / ((x-1)^3*(x+1)*(x^2+1)^2). - _Colin Barker_, Mar 31 2013
%o (Haskell)
%o a008217 n = a008217_list !! n
%o a008217_list = zipWith (*) (tail qs) qs where qs = map (`div` 4) [0..]
%o -- _Reinhard Zumkeller_, Oct 09 2011
%o (PARI) a(n) = floor(n/4)*floor((n+1)/4); /* _Joerg Arndt_, Mar 31 2013 */
%o (Python)
%o def A008217(n): return (n>>2)*(n+1>>2) # _Chai Wah Wu_, Feb 02 2023
%Y Cf. A008133.
%K nonn
%O 0,8
%A _N. J. A. Sloane_.
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