A235710 -id:A235710 - cp's OEIS frontend

A279359 Even numbers whose sum of proper divisors is a Fibonacci number.

2, 4, 10, 18, 36, 62, 90, 902, 1214, 2936, 3436, 325726, 378646, 646840, 5432174, 273222344, 285775216, 1411668430, 1416411790, 2586905784, 34620518734, 564515976926, 811882646208, 1326864647898, 1548008754928, 2063984735284, 28933238284712, 29040521400152, 31260018191912, 31586954074712, 160595113092766, 164736642645358, 180312970059936

Offset: 1

Altug Alkan, Dec 16 2016

nonn

What is the asymptotic behavior of this sequence?

			18 is a term because 1 + 2 + 3 + 6 + 9 = 21 is a Fibonacci number.

Cf. A000045, A001065, A235710, A272412.

isFibonacci(n)=my(k=n^2); issquare(k+=(k+1)<<2) || (n>0 && issquare(k-8));
is(n)=isFibonacci(sigma(n)-n)&&n%2==0

a(18)-a(20) from Amiram Eldar, Oct 18 2019

a(21)-a(33) from Max Alekseyev, May 23 2025

A291373 a(n) is the smallest number k such that A001065(k) = A002110(n), or 0 if no such k exists.

Original entry on oeis.org

2, 0, 6, 841, 0, 1722, 30018, 0, 0, 0, 4057230930, 0, 0, 92568222856376123089883329681

Offset: 0

Altug Alkan, Aug 23 2017

For n in A057704, 0 < a(n) <= (A002110(n)-1)^2. - Max Alekseyev, Sep 01 2025

			a(5) = 1722 because sigma(1722) - 1722 = 2*3*5*7*11 = A002110(5) and 1722 is the least number with this property.

Cf. A001065, A002110, A057704, A070015, A116017, A153076, A235710, A244444, A279359, A291356, A378099.

a(n) = A070015(A002110(n)). - Michel Marcus, Aug 25 2017

a(7) and a(10) from Giovanni Resta, Aug 23 2017

a(8)-a(9), a(11)-a(13) from Max Alekseyev, Sep 04 2025

cp's OEIS Frontend

A279359 Even numbers whose sum of proper divisors is a Fibonacci number.

Views

Author

Keywords

Comments

Examples

Crossrefs

Programs

PARI

Extensions