This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A077581 #18 Dec 15 2015 00:58:25 %S A077581 1,1,3,1,2,4,1,3,5,7,1,2,3,4,6,1,5,7,11,13,17,1,2,3,4,5,6,8,1,3,5,7,9, %T A077581 11,13,15,1,2,4,5,7,8,10,11,13,1,3,7,9,11,13,17,19,21,23,1,2,3,4,5,6, %U A077581 7,8,9,10,12,1,5,7,11,13,17,19,23,25,29,31,35,1,2,3,4,5,6,7,8,9,10,11,12 %N A077581 Triangle in which row n contains the n smallest numbers starting from 1 and coprime to n. %C A077581 A247815 and A247892 give number of primes and nonprimes per row. - _Reinhard Zumkeller_, Sep 26 2014 %H A077581 Reinhard Zumkeller, <a href="/A077581/b077581.txt">Rows n = 1..125 of triangle, flattened</a> %e A077581 1; %e A077581 1, 3; %e A077581 1, 2, 4; %e A077581 1, 3, 5, 7; %e A077581 1, 2, 3, 4, 6; %e A077581 1, 5, 7, 11, 13, 17; %e A077581 1, 2, 3, 4, 5, 6, 8; %e A077581 1, 3, 5, 7, 9, ... %t A077581 row[n_] := Take[Select[Range[n^2], GCD[ #, n]==1&], n]; Join@@row/@Range[13] %o A077581 (Haskell) %o A077581 a077581 n k = a077581_tabl !! (n-1) !! (k-1) %o A077581 a077581_row n = a077581_tabl !! (n-1) %o A077581 a077581_tabl = map (\x -> take x [z | z <- [1..], gcd x z == 1]) [1..] %o A077581 -- _Reinhard Zumkeller_, Sep 26 2014 %Y A077581 Cf. A069213, A077582. %Y A077581 Cf. A247798 (central terms), A247815, A247892. %Y A077581 Cf. A077664. %K A077581 nonn,tabl,easy,look %O A077581 1,3 %A A077581 _Amarnath Murthy_, Nov 14 2002 %E A077581 More terms from _Sascha Kurz_, Jan 11 2003