A279950 List of ordered pairs (x, y) from A279812.
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
Offset: 1
Keywords
Examples
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.
Crossrefs
Cf. A279812.
Programs
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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 *)
Comments