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%I #13 Dec 07 2017 09:48:35
%S 0,0,1,0,1,0,0,0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,
%T 0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,
%U 0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
%N a(n) = f(f(n+1)) - f(f(n)), where f(m) = pi(m) = A000720(m), with f(0) = 0.
%C Right-shifted sequence is characteristic function of prime-indexed primes (A006450). - _Franklin T. Adams-Watters_, Nov 17 2006
%H Antti Karttunen, <a href="/A111406/b111406.txt">Table of n, a(n) for n = 0..65557</a>
%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%o (PARI) A111406(n) = (primepi(primepi(n+1)) - primepi(primepi(n))); \\ _Antti Karttunen_, Dec 07 2017
%Y Cf. A000720, A006450.
%K nonn
%O 0,1
%A _N. J. A. Sloane_, Nov 12 2005
%E Missing right parenthesis added to the formula and case f(0) clarified by _Antti Karttunen_, Dec 07 2017