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a(n)=pi(n)*[pi(n)-pi(n-2)] where pi(n)=A000720(n).
1

%I #2 Oct 15 2013 22:32:21

%S 0,1,4,2,3,3,4,4,0,0,5,5,6,6,0,0,7,7,8,8,0,0,9,9,0,0,0,0,10,10,11,11,

%T 0,0,0,0,12,12,0,0,13,13,14,14,0,0,15,15,0,0,0,0,16,16,0,0,0,0,17,17,

%U 18,18,0,0,0,0,19,19,0,0,20,20,21,21,0,0,0,0,22,22,0,0,23,23,0,0,0,0,24,24

%N a(n)=pi(n)*[pi(n)-pi(n-2)] where pi(n)=A000720(n).

%Y Cf. A049084, A000720, A010051, A000027, A090113.

%K nonn

%O 1,3

%A _Labos Elemer_, Jan 08 2004