# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a249917 Showing 1-1 of 1 %I A249917 #10 Aug 01 2019 03:48:01 %S A249917 1,2,10,3,14,15,4,20,18,12,5,22,33,44,95,7,26,45,48,145,6,8,34,51,76, %T A249917 200,30,91,9,38,69,88,295,42,196,56,11,46,72,92,395,54,273,112,153,13, %U A249917 52,87,108,445,66,287,184,288,40,16,58,99,124,475,78,455,248,459,190,473 %N A249917 Square array read by antidiagonals where the n-th row lists the integers x such that gcd(x, sigma(x)) = n. %C A249917 First line is A014567 and first column is A074391. %C A249917 This is a permutation of the positive integers. %H A249917 Index entries for sequences that are permutations of the natural numbers %e A249917 Array begins: %e A249917 1, 2, 3, 4, 5, 7, 8, ... %e A249917 10, 14, 20, 22, 26, 34, 38, ... %e A249917 15, 18, 33, 45, 51, 69, 72, ... %e A249917 12, 44, 48, 76, 88, 92, 108, ... %e A249917 95, 145, 200, 295, 395, 445, 475, ... %e A249917 6, 30, 42, 54, 66, 78, 102, ... %e A249917 91, 196, 273, 287, 455, 581, 637, ... %e A249917 56, 112, 184, 248, 368, 376, 432, ... %e A249917 ... %o A249917 (PARI) triangle(nn) = {v = vector(nn); for (n=1, nn, for (k=1, n, if (! v[k], x = 1, x = v[k] + 1); while (gcd(sigma(x), x) != k, x++); print1(x, ", "); v[k] = x;); print(););} %Y A249917 Cf. A009194 (gcd(n, sigma(n))), A014567 (gcd(n, sigma(n))=1), A074391 (smallest x such that gcd(x, sigma(x)) is n), %K A249917 nonn,tabl %O A249917 1,2 %A A249917 _Michel Marcus_, Jan 14 2015 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE