A124739 a(n) = sum of those positive integers which are coprime to both n and n+1 and which are <= n.

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, 108, 114, 168, 91, 120, 225, 170, 153, 199, 144, 216, 305, 221, 175, 320, 211, 252, 397, 261, 249, 506, 337, 342, 423, 351, 403, 624, 433, 410, 483, 431, 493, 812, 421, 480

Offset: 1

Author

Leroy Quet, Nov 06 2006

Keywords

• nonn

Examples

			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.
		

Crossrefs

Cf. A057475, A124738, A124740, A124741.

Programs

Mathematica

f[n_] := Plus @@ Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &];Table[f[n], {n, 60}] (* Ray Chandler, Nov 10 2006 *)

Extensions

Extended by Ray Chandler, Nov 10 2006