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Search: id:A163122
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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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+0
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
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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{n : n in A002808, and A001065(n) = A069250(n)}. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 27 2009
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EXAMPLE
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840 is in the list. 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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CROSSREFS
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Sequence in context: A070807 A046352 A046355 this_sequence A050655 A117098 A077136
Adjacent sequences: A163119 A163120 A163121 this_sequence A163123 A163124 A163125
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KEYWORD
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nonn,base
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AUTHOR
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Claudio L Meller (claudiomeller(AT)gmail.com), Jul 21 2009
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EXTENSIONS
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Keyword:base added by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 27 2009
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