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Irregular table where the n-th row consists of those positive integers which are coprime to both n and n+1 and which are <= n.
5

%I #10 Oct 11 2019 11:00:00

%S 1,1,1,1,3,1,1,5,1,3,5,1,5,7,1,7,1,3,7,9,1,5,7,1,5,7,11,1,3,5,9,11,1,

%T 11,13,1,7,11,13,1,3,5,7,9,11,13,15,1,5,7,11,13,1,5,7,11,13,17,1,3,7,

%U 9,11,13,17,1,11,13,17,19,1,5,13,17,19,1,3,5,7,9,13,15,17,19,21,1,5,7,11,13

%N Irregular table where the n-th row consists of those positive integers which are coprime to both n and n+1 and which are <= n.

%C The n-th row has A057475(n) terms.

%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) make up the row of A124738.

%t f[n_] := Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &]; Flatten[Table[f[n], {n, 23}]] (* _Ray Chandler_, Nov 10 2006 *)

%Y Cf. A057475, A124739, A124740, A124741.

%K nonn,tabf

%O 1,5

%A _Leroy Quet_, Nov 06 2006

%E Extended by _Ray Chandler_, Nov 10 2006