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 A249917 Square array read by antidiagonals where the n-th row lists the integers x such that gcd(x, sigma(x)) = n. 1

%I

%S 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 200,30,91,9,38,69,88,295,42,196,56,11,46,72,92,395,54,273,112,153,13,

%U 52,87,108,445,66,287,184,288,40,16,58,99,124,475,78,455,248,459,190,473

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

%C First line is A014567 and first column is A074391.

%C This is a permutation of the positive integers.

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

%e Array begins:

%e 1, 2, 3, 4, 5, 7, 8, ...

%e 10, 14, 20, 22, 26, 34, 38, ...

%e 15, 18, 33, 45, 51, 69, 72, ...

%e 12, 44, 48, 76, 88, 92, 108, ...

%e 95, 145, 200, 295, 395, 445, 475, ...

%e 6, 30, 42, 54, 66, 78, 102, ...

%e 91, 196, 273, 287, 455, 581, 637, ...

%e 56, 112, 184, 248, 368, 376, 432, ...

%e ...

%o (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 Cf. A009194 (gcd(n, sigma(n))), A014567 (gcd(n, sigma(n))=1), A074391 (smallest x such that gcd(x, sigma(x)) is n),

%K nonn,tabl

%O 1,2

%A _Michel Marcus_, Jan 14 2015

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Last modified May 14 13:50 EDT 2021. Contains 343884 sequences. (Running on oeis4.)