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A274062 Even numbers such that the sum of the odd divisors is a Fibonacci number F and the sum of the even divisors is 2F. 0
2, 14, 18, 230, 238, 4958, 53430, 57930, 64506, 65586, 68226, 70730, 77270, 78638, 81926, 84986, 88826, 90446, 91306, 1006350, 1248054, 1341950, 18177726, 19033854, 19603430, 21044030, 22356798, 22395522, 22876730, 23954170, 24241966, 24840710, 24883910, 25285666, 25306246 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n)== 2,6,10 (mod 12) i.e. a(n)== 2 (mod 4) so this sequence is a subsequence of A016825 (of which 3|sigma(A016825(n)).

The corresponding Fibonacci numbers F are 1, 8, 13, 144, 144, 2584, 46368, 46368, 46368, 46368,...  with index 1 (or 2), 6, 7, 12, 12, 18, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 30, 30, 30

The sequence is generalizable with the following definition: even numbers such that the sum of the odd divisors is a Fibonacci number F and the sum of the even divisors is (2^k -2)*F = A000918(k)*F with k>1. The corresponding sequences b(n,k) are of the form b(n,k) = a(n)*2^(k-2) where a(n) is the primitive sequence.

LINKS

Table of n, a(n) for n=1..35.

EXAMPLE

18 is in the sequence because: its divisors are {1, 2, 3, 6, 9, 18}; the sum of its odd divisors is 1 + 3 + 9 = 13, a Fibonacci number, and the sum of its even divisors is 2 + 6 + 18 = 26 = 2*13.

MAPLE

with(numtheory):

for n from 2 by 2  to 10^7 do:

   y:=divisors(n):n1:=nops(y):s0:=0:s1:=0:

     for k from 1 to n1 do:

       if irem(y[k], 2)=0

        then

        s0:=s0+ y[k]:

        else

        s1:=s1+ y[k]:

      fi:

     od:

     if s0=2*s1

      then

      ii:=0:

        x:=sqrt(5*s1^2+4):y:=sqrt(5*s1^2-4):

         if x=floor(x) or y=floor(y)

          then

          printf ( "%d %d \n", n, s1):

           else

          fi:

        fi:

     od:

MATHEMATICA

t = Fibonacci@ Range@ 40; Select[Range[2, 2*10^6, 4], Function[d, And[Total@ Select[d, EvenQ] == 2 #, MemberQ[t, #]] &@ Total@ Select[d, OddQ]]@ Divisors@ # &] (* Michael De Vlieger, Jun 09 2016 *)

PROG

(PARI) isok(n) = sod = sumdiv(n, d, d*(d % 2)); (2*sod == sumdiv(n, d, d*(1-(d % 2)))) && (issquare(5*sod^2-4) || issquare(5*sod^2+4)); \\ Michel Marcus, Jun 09 2016

CROSSREFS

Cf. A000045, A000918, A016825, A087943.

Sequence in context: A322955 A266388 A032476 * A059205 A298002 A217075

Adjacent sequences:  A274059 A274060 A274061 * A274063 A274064 A274065

KEYWORD

nonn

AUTHOR

Michel Lagneau, Jun 09 2016

EXTENSIONS

a(23)-a(35) from Michel Marcus, Jun 14 2016

STATUS

approved

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Last modified October 1 00:42 EDT 2020. Contains 337440 sequences. (Running on oeis4.)