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A072228
Numbers k such that k equals the sum of the reverses of the proper divisors of k.
3
6, 244, 285, 133857, 141635817, 273722772124
OFFSET
1,1
COMMENTS
I call these numbers "anti-perfect" (compare with the picture-perfect numbers A069942).
a(7) > 10^12. - Giovanni Resta, Apr 07 2017
EXAMPLE
The proper divisors of 285 are 1, 3, 5, 15, 19, 57, 95, with sum of reverses = 1 + 3 + 5 + 51 + 91 + 75 + 59 = 285. Therefore 285 is anti-perfect.
MATHEMATICA
f[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Do[ If[n == Apply[Plus, Map[f, Drop[Divisors[n], -1]]], Print[n]], {n, 2, 10^7}]
Select[Range[15*10^7], Total[IntegerReverse[Most[Divisors[#]]]]==#&] (* Requires Mathematica version 10 or later *) (* The program takes a long time to run *) (* Harvey P. Dale, Aug 31 2016 *)
CROSSREFS
Sequence in context: A156936 A231019 A254009 * A322559 A229631 A206307
KEYWORD
base,more,nonn,nice
AUTHOR
Joseph L. Pe, Jul 05 2002
EXTENSIONS
One more term from Farideh Firoozbakht, Dec 23 2004
a(6) from Giovanni Resta, Apr 07 2017
STATUS
approved