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 A240062 Square array read by antidiagonals in which T(n,k) is the n-th number j with the property that the symmetric representation of sigma(j) has k parts. 17
 1, 2, 3, 4, 5, 9, 6, 7, 15, 21, 8, 10, 25, 27, 63, 12, 11, 35, 33, 81, 147, 16, 13, 45, 39, 99, 171, 357, 18, 14, 49, 51, 117, 189, 399, 903, 20, 17, 50, 55, 153, 207, 441, 987, 2499, 24, 19, 70, 57, 165, 243, 483, 1029, 2709, 6069, 28, 22, 77, 65, 195, 261, 513, 1113 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This is a permutation of the positive integers. All odd primes are in column 2 (together with some even composite numbers) because the symmetric representation of sigma(prime(i)) is [m, m], where m = (1 + prime(i))/2, for i >= 2. The union of all odd-indexed columns gives A071562, the positive integers that have middle divisors. The union of all even-indexed columns gives A071561, the positive integers without middle divisors. - Omar E. Pol, Oct 01 2018 LINKS EXAMPLE Array begins: 1,   3,   9,  21,  63, 147, 357,  903, 2499, 6069... 2,   5,  15,  27,  81, 171, 399,  987, 2709... 4,   7,  25,  33,  99, 189, 441, 1029... 6,  10,  35,  39, 117, 207, 483... 8,  11,  45,  51, 153, 243... 12, 13,  49,  55, 165... 16, 14,  50,  57... 18, 17,  70... 20, 19... 24... CROSSREFS For programs see A237271 and A237593. Row 1 is A239663. Column 1 is A238443 = A174973. Column 2 is A239929. Column 3 is A279102, and column 4 is A280107. - Omar E. Pol, Dec 27 2016 For more information see A239663 and A239665. Cf. A000203, A006254, A065091, A067742, A071561, A071562, A196020, A236104, A235791, A237048, A237270, A237271, A238443, A239660, A239929, A239931-A239934, A245092, A262626, A319529, A319796, A319801, A319802. Sequence in context: A166276 A101544 A171100 * A255129 A119586 A095904 Adjacent sequences:  A240059 A240060 A240061 * A240063 A240064 A240065 KEYWORD nonn,tabl AUTHOR Omar E. Pol, Apr 06 2014 EXTENSIONS a(n) > 128 from Michel Marcus, Apr 08 2014 STATUS approved

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Last modified May 7 20:36 EDT 2021. Contains 343652 sequences. (Running on oeis4.)