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A279950 List of ordered pairs (x, y) from A279812. 1
440, 568, 2368, 2420, 5240, 5848, 10040, 11128, 12464, 12736, 21488, 21712, 24570, 29190, 34592, 36832, 126040, 152168, 133856, 133984, 134190, 142290, 139230, 175266, 159500, 177460, 200970, 248310, 244530, 279630, 244736, 246304, 283328, 306352, 284620, 337460 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The terms of the sequence A279812 are given in increasing order. The terms of this sequence are ordered pairs (a(2n-1), a(2n)) where a(2n-1) < a(2n+1) < a(2n+3) < ...

LINKS

Table of n, a(n) for n=1..36.

EXAMPLE

The pair (a(1), a(2)) = (440, 568) is in the sequence because the even proper divisors of 440 are 2, 4, 8, 10, 20, 22, 40, 44, 88, 110, 220 with sum = 568 and the proper divisors of 568 are 2, 4, 8, 142, 284 with sum = 440.

MATHEMATICA

f[n_] := Total@ DeleteCases[Most@ Divisors@ n, d_ /; OddQ@ d]; DeleteCases[Union@ Table[If[# == 0, {0, 0}, Sort@ {n, # Boole[f@ # == n]}] &@ f@ n, {n, 2, 10^6}], w_ /; Or[First@ w == 0, MatchQ @@ w]] // Flatten (* Michael De Vlieger, Dec 23 2016 *)

CROSSREFS

Cf. A279812.

Sequence in context: A345555 A345809 A279812 * A072604 A158319 A250879

Adjacent sequences:  A279947 A279948 A279949 * A279951 A279952 A279953

KEYWORD

nonn

AUTHOR

Michel Lagneau, Dec 23 2016

STATUS

approved

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Last modified December 2 05:01 EST 2021. Contains 349437 sequences. (Running on oeis4.)