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%I #11 Oct 12 2023 12:34:35
%S 4,6,8,9,10,12,14,15,16,18,21,22,25,27,33,35,44,49,55,66,77,88,99,121,
%T 202,242,262,302,303,362,363,382,393,403,404,453,484,505,524,543,573,
%U 605,606,626,655,689,706,707,726,746,755,766,783,786,808,840,847,905
%N Composite numbers for which the sum of proper divisors equals the sum of the digit-reversed proper divisors.
%H Harvey P. Dale, <a href="/A163122/b163122.txt">Table of n, a(n) for n = 1..1000</a>
%F {n : n in A002808, and A001065(n) = A069250(n)}. - _R. J. Mathar_, Jul 27 2009
%e 840 is in the sequence: the sum of its proper divisors is
%e 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 10 + 12 + 14 + 15 + 20 + ... + 280 + 420 = A001065(840) = 2040,
%e and the sum of the reversed proper divisors is
%e 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 1 + 21 + 41 + 51 + 2 + ... + 82 + 24 = A069250(840) = 2040.
%p read("transforms") ; A001065 := proc(n) numtheory[sigma](n)-n ; end:
%p A069250 := proc(n) local pdvs ,a,d ; pdvs := numtheory[divisors](n) minus {n} ; a := 0 ; for d in pdvs do a := a+digrev(d) ; od: a ; end:
%p for n from 4 to 1000 do if not isprime(n) and A001065(n) = A069250(n) then printf("%d,",n) ; fi; od: # _R. J. Mathar_, Jul 27 2009
%t Select[Range[1000],CompositeQ[#]&&DivisorSigma[1,#]-#==Total[IntegerReverse/@ Most[ Divisors[ #]]]&] (* _Harvey P. Dale_, Oct 12 2023 *)
%K nonn,base
%O 1,1
%A _Claudio Meller_, Jul 21 2009
%E Keyword:base added by _R. J. Mathar_, Jul 27 2009
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