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 A233773 Triangle read by rows in which row n lists the proper divisors of n together with -n. 2
 -1, 1, -2, 1, -3, 1, 2, -4, 1, -5, 1, 2, 3, -6, 1, -7, 1, 2, 4, -8, 1, 3, -9, 1, 2, 5, -10, 1, -11, 1, 2, 3, 4, 6, -12, 1, -13, 1, 2, 7, -14, 1, 3, 5, -15, 1, 2, 4, 8, -16, 1, -17, 1, 2, 3, 6, 9, -18, 1, -19, 1, 2, 4, 5, 10, -20, 1, 3, 7, -21, 1, 2, 11, -22, 1, -23 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The same as A027750 but with the last term of every row multiplied by -1. The sum of row n gives the abundance of n. LINKS Eric Weisstein's World of Mathematics, Abundance Eric Weisstein's World of Mathematics, Quasiperfect Number EXAMPLE Written as an irregular triangle in which row n has length A000005(n) the sequence begins: -1; 1, -2; 1, -3; 1, 2, -4; 1, -5; 1, 2, 3, -6; 1, -7; 1, 2, 4, -8; 1, 3, -9; 1, 2, 5, -10; 1, -11; 1, 2, 3, 4, 6, -12; ... MATHEMATICA Flatten[Table[Join[{Most[Divisors[n]]}, {-n}], {n, 30}]] (* Harvey P. Dale, Feb 20 2016 *) CROSSREFS Row sums give A033880. Cf. A000005, A000203, A000396, A001065, A005100, A005101, A027750, A027751, A033879. Cf. A137510, A163870. Sequence in context: A169896 A210208 A162306 * A027750 A275055 A254679 Adjacent sequences:  A233770 A233771 A233772 * A233774 A233775 A233776 KEYWORD sign,tabf AUTHOR Omar E. Pol, Dec 31 2013 STATUS approved

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Last modified August 11 00:32 EDT 2020. Contains 336403 sequences. (Running on oeis4.)