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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

Table of n, a(n) for n=1..76.

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 February 21 04:22 EST 2018. Contains 299389 sequences. (Running on oeis4.)