A002221 - OEIS

%I M3861 N1583 #26 May 24 2016 05:28:48

%S 1,5,15,55,140,448,1022,2710,6048,14114,28831,64091,123649,251295,

%T 476835,916972,1654044,3080159,5377431,9624588,16490017,28433473,

%U 47423409,80279375

%N a(n) is the number of partitions of 4n that can be obtained by adding together four (not necessarily distinct) partitions of n.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H N. Metropolis and P. R. Stein, <a href="http://dx.doi.org/10.1016/S0021-9800(70)80091-6">An elementary solution to a problem in restricted partitions</a>, J. Combin. Theory, 9 (1970), 365-376.

%Y See A002219 for further details. Cf. A002220, A002222, A213074.

%Y A column of A213086.

%K nonn,more

%O 1,2

%A _N. J. A. Sloane_

%E Edited by _N. J. A. Sloane_, Jun 03 2012

%E a(12)-a(16) from _Alois P. Heinz_, Jul 10 2012

%E a(17)-a(24) from _Sean A. Irvine_, Sep 05 2013