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%I #8 Jan 09 2024 16:56:14
%S 0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1,0,
%T 0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,
%U 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
%N a(n) = 1 if n satisfies the arithmetic differential equation 2n" - n' - 4 = 0, otherwise 0. Cf. A003415.
%H Antti Karttunen, <a href="/A368701/b368701.txt">Table of n, a(n) for n = 1..100023</a>
%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%F a(n) = [0 == 2*A068346(n) - A003415(n) - 4], where [ ] is the Iverson bracket.
%o (PARI)
%o A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));
%o A368701(n) = (4==(2*A003415(A003415(n)) - A003415(n)));
%Y Characteristic function of A334261.
%Y Cf. A001248, A003415, A068346.
%K nonn
%O 1
%A _Antti Karttunen_, Jan 09 2024
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