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%I #7 Mar 20 2018 19:02:15
%S 0,0,1,0,1,0,-13,4,23,0,1,0,-25,4,35,0,1,0,-37,4,47,0,-91,-42,9,62,
%T 117,0,1,0,-123,-58,9,78,149,0,-73,4,83,0,1,0,-85,4,95,0,-187,-90,9,
%U 110,213,0,-211,-102,9,122,237,0,1,0,-243,-118,9,138,269,0,-133,4,143,0,1,0,-291,-142,9,162,317,0,-157,4,167,0,-331,-162,9
%N a(n) = n^2 - primefloor(n)*primeceiling(n).
%C a(n)= 0 iff n is prime.
%H Antti Karttunen, <a href="/A056139/b056139.txt">Table of n, a(n) for n = 2..65537</a>
%F a(n) = n^2 - A007917(n)*A007918(n) = A000290(n) - A030664(n).
%e a(3)=3^2-3*3=0, a(4)=4^2-3*5=1
%o (PARI)
%o A030664(n) = if (n < 2, 1, precprime(n)*nextprime(n)); \\ From A030664
%o A056139(n) = (n^2 - A030664(n)); \\ _Antti Karttunen_, Mar 20 2018
%Y Cf. A007917, A007918, A030664, A056140, A056141.
%K easy,sign
%O 2,7
%A _Henry Bottomley_, Jun 15 2000
%E More terms from _Antti Karttunen_, Mar 20 2018
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