cp's OEIS Frontend

A249917 Square array read by antidiagonals where the n-th row lists the integers x such that gcd(x, sigma(x)) = n.

%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 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%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