A032262 - OEIS

%I #21 Aug 26 2019 11:46:30

%S 1,1,2,5,17,83,557,4715,47357,545963,7087517,102248075,1622633597,

%T 28091569643,526858352477,10641342978635,230283190994237,

%U 5315654682014123,130370767029201437,3385534663256976395

%N Number of ways to partition n labeled elements into pie slices allowing the pie to be turned over.

%H Andrew Howroyd, <a href="/A032262/b032262.txt">Table of n, a(n) for n = 0..200</a>

%H C. G. Bower, <a href="/transforms2.html">Transforms (2)</a>

%F a(n) = 2^(n-2) + A000670(n-1) for n >= 2. - _N. J. A. Sloane_, Jan 17 2008

%F a(n) = 2^(n-1) + Sum_{k >= 3} Stirling_2(n,k)*(k-1)!/2 for n >= 1. - _N. J. A. Sloane_, Jan 17 2008

%F "DIJ" (bracelet, indistinct, labeled) transform of 1, 1, 1, 1, ... (see Bower link).

%F E.g.f.: 1 + (g(x) + g(x)^2/2 - log(1-g(x)))/2 where g(x) = exp(x) - 1. - _Andrew Howroyd_, Sep 12 2018

%e For n = 4 we have the following "pies":

%e . 1

%e ./ \

%e 2 . 3 . 12 .. 12 . 123 .1234

%e .\ / .. / \ .(..)..(..)

%e . 4 .. 3--4 . 34 .. 4

%e .(3)....(6)...(3)..(4)...(1) Total a(4) = 17

%t a[0] = a[1] = 1; a[n_] := 2^(n-2) + HurwitzLerchPhi[1/2, 1-n, 0]/2;

%t Array[a, 20, 0] (* _Jean-François Alcover_, Aug 26 2019 *)

%o (PARI) seq(n)={my(p=exp(x + O(x*x^n))-1); Vec(1 + serlaplace(p + p^2/2 - log(1-p))/2)} \\ _Andrew Howroyd_, Sep 12 2018

%Y Row sums of triangle A133800.

%K nonn

%O 0,3

%A _Christian G. Bower_

%E Edited by _N. J. A. Sloane_, Jan 17 2008

%E a(0)=1 prepended by _Andrew Howroyd_, Sep 12 2018