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A163122
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Composite numbers for which the sum of proper divisors equals the sum of the digit-reversed proper divisors.
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1
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4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 21, 22, 25, 27, 33, 35, 44, 49, 55, 66, 77, 88, 99, 121, 202, 242, 262, 302, 303, 362, 363, 382, 393, 403, 404, 453, 484, 505, 524, 543, 573, 605, 606, 626, 655, 689, 706, 707, 726, 746, 755, 766, 783, 786, 808, 840, 847, 905
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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840 is in the sequence: the sum of its proper divisors is
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 10 + 12 + 14 + 15 + 20 + ... + 280 + 420 = A001065(840) = 2040,
and the sum of the reversed proper divisors is
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 1 + 21 + 41 + 51 + 2 + ... + 82 + 24 = A069250(840) = 2040.
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MAPLE
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read("transforms") ; A001065 := proc(n) numtheory[sigma](n)-n ; end:
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:
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
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MATHEMATICA
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Select[Range[1000], CompositeQ[#]&&DivisorSigma[1, #]-#==Total[IntegerReverse/@ Most[ Divisors[ #]]]&] (* Harvey P. Dale, Oct 12 2023 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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