A163122 Composite numbers for which the sum of proper divisors equals the sum of the digit-reversed proper divisors.

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

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

{n : n in A002808, and A001065(n) = A069250(n)}. - R. J. Mathar, Jul 27 2009

Example

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.

Maple

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

Mathematica

Select[Range[1000], CompositeQ[#]&&DivisorSigma[1, #]-#==Total[IntegerReverse/@ Most[ Divisors[ #]]]&] (* Harvey P. Dale, Oct 12 2023 *)

Crossrefs

Sequence in context: A046352 A046355 A335419 * A329149 A202259 A050655

Adjacent sequences: A163119 A163120 A163121 * A163123 A163124 A163125

Keyword

nonn,base

Author

Claudio Meller, Jul 21 2009

Extensions

Keyword:base added by R. J. Mathar, Jul 27 2009

Status

approved