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%I #9 Oct 11 2019 10:59:38
%S 1,1,1,4,1,6,9,13,8,20,13,24,29,25,32,64,37,54,61,61,55,110,73,91,111,
%T 108,114,168,91,120,225,170,153,199,144,216,305,221,175,320,211,252,
%U 397,261,249,506,337,342,423,351,403,624,433,410,483,431,493,812,421,480
%N a(n) = sum of those positive integers which are coprime to both n and n+1 and which are <= n.
%e The positive integers which are coprime to 8 and which are <= 8 are 1,3,5,7. The integers which are coprime to 9 and which are <= 9 are 1, The integers in both these sequences (1,5,7) are added get a(8) = 13.
%t f[n_] := Plus @@ Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &];Table[f[n], {n, 60}] (* _Ray Chandler_, Nov 10 2006 *)
%Y Cf. A057475, A124738, A124740, A124741.
%K nonn
%O 1,4
%A _Leroy Quet_, Nov 06 2006
%E Extended by _Ray Chandler_, Nov 10 2006