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A099187 Let D(n) = n*(9*n^2-9*n+2)/2 then a(k+1) = D(a(k)) and a(0) = 1.

%I A099187 #22 Jun 09 2023 11:04:00
%S A099187 1,20,34220,180318314012420,
%T A099187 26383476911029432816173777932463879690054620
%N A099187 Let D(n) = n*(9*n^2-9*n+2)/2 then a(k+1) = D(a(k)) and a(0) = 1.
%H A099187 Michel Marcus, <a href="/A099187/b099187.txt">Table of n, a(n) for n = 0..6</a>
%H A099187 Hyun Kwang Kim, <a href="http://dx.doi.org/10.1090/S0002-9939-02-06710-2">On Regular Polytope Numbers</a>, Proc. Amer. Math. Soc., 131 (2003), 65-75.
%F A099187 Let D(n) = n*(9*n^2-9*n+2)/2 then a(k+1) = D(a(k)) and a(0) = 1.
%t A099187 Dod[n_]:= n*(9*n^2-9*n+2)/2;
%t A099187 a[n_]:= If[n==0, Dod[1], If[n==1, Dod[2], Dod[a[n-1]]]];
%t A099187 Table[a[n], {n, 0, 4}] (* _G. C. Greubel_, Mar 22 2019 *)
%o A099187 (PARI) dod(n) = n*(9*n^2-9*n+2)/2;
%o A099187 a(n) = if (n==0, 1, if (n==1, dod(2), dod(a(n-1)))); \\ _Michel Marcus_, Dec 14 2015
%Y A099187 Cf. A007501, A006566.
%K A099187 easy,nonn
%O A099187 1,2
%A A099187 _Jonathan Vos Post_, Nov 15 2004