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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
 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, 200, 30, 91, 9, 38, 69, 88, 295, 42, 196, 56, 11, 46, 72, 92, 395, 54, 273, 112, 153, 13, 52, 87, 108, 445, 66, 287, 184, 288, 40, 16, 58, 99, 124, 475, 78, 455, 248, 459, 190, 473 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS First line is A014567 and first column is A074391. This is a permutation of the positive integers. LINKS EXAMPLE Array begins:    1,   2,  3,    4,   5,   7,   8, ...   10,  14,  20,  22,  26,  34,  38, ...   15,  18,  33,  45,  51,  69,  72, ...   12,  44,  48,  76,  88,  92, 108, ...   95, 145, 200, 295, 395, 445, 475, ...    6,  30,  42,  54,  66,  78, 102, ...   91, 196, 273, 287, 455, 581, 637, ...   56, 112, 184, 248, 368, 376, 432, ...   ... PROG (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(); ); } CROSSREFS Cf. A009194 (gcd(n, sigma(n))), A014567 (gcd(n, sigma(n))=1), A074391 (smallest x such that gcd(x, sigma(x)) is n), Sequence in context: A239136 A239137 A252758 * A176577 A247476 A245062 Adjacent sequences:  A249914 A249915 A249916 * A249918 A249919 A249920 KEYWORD nonn,tabl AUTHOR Michel Marcus, Jan 14 2015 STATUS approved

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Last modified June 21 04:47 EDT 2021. Contains 345355 sequences. (Running on oeis4.)