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%I #10 Aug 01 2020 11:37:32
%S 1,12,1,2,3,3,2,2,5,2,3,3,3,4,1,4,15,8,8,4,3,48,23,6,5,2,8,8,5,24,8,2,
%T 11,6,4,6,20,16,6,8,7,32,6,6,6,33,8,7,8,16,13,4,15,25,16,14,6,27,35,
%U 33,16,8,6,4,7,105,67,12,15,2,71,6,18,2,7,15,16,6
%N a(n) is the least k such that the distance between (n, phi(n)) and (n+k, phi(n+k)) is an integer (i.e., k^2 + (phi(n+k) - phi(n))^2 is a square), or 0 if none exists.
%e 12^2 + (phi(2+12) - phi(2))^2 = 13^2 and k = 12 is the least natural number achieving this, so a(2) = 12.
%o (PARI) a(n) = for(k=1, oo, if(issquare(k^2 + (eulerphi(n+k) - eulerphi(n))^2), return(k))); \\ _Jinyuan Wang_, Jul 30 2020
%Y Cf. A000010.
%K nonn,less
%O 1,2
%A _Joseph L. Pe_, Jan 18 2002
%E More terms from _Jinyuan Wang_, Jul 30 2020
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