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Number of partitions of n with equal nonzero number of parts congruent to each of 1 and 2 (mod 3)
1

%I #8 Dec 07 2016 09:43:57

%S 0,0,0,1,0,0,4,0,0,11,0,0,27,0,0,59,0,0,123,0,0,241,0,0,458,0,0,838,0,

%T 0,1498,0,0,2608,0,0,4459,0,0,7473,0,0,12339,0,0,20058,0,0,32197,0,0,

%U 51027,0,0,80003,0,0,124092,0,0,190683,0,0,290322,0,0,438392,0,0,656681,0,0

%N Number of partitions of n with equal nonzero number of parts congruent to each of 1 and 2 (mod 3)

%t equalQ[partit_] := With[{t = Total[Switch[Mod[#, 3], 0, {1, 0, 0}, 1, {0, 1, 0}, 2, {0, 0, 1}]& /@ partit]}, t[[2]] > 0 && t[[2]] == t[[3]]]; a[n_] := If[Mod[n, 3] != 0, 0, Select[IntegerPartitions[n], equalQ] // Length]; a[0] = 0; Table[an = a[n]; Print["a(", n, ") = ", an]; an, {n, 0, 71}] (* _Jean-François Alcover_, Dec 07 2016 *)

%Y Cf. A035593.

%K nonn

%O 0,7

%A _Olivier Gérard_