This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A274380 A 4-cycle of the iterated sum of deficient divisors function. 5
 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48, 34, 54, 42, 48 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This cycle is generated in a similar way to the aliquot sequences (or sociable chains) that are generated by the sum of proper divisors function.  This cycle appears to be one of just two cycles of length (or order) 4 that are generated by the sum of deficient divisors function. If sigma(N) is the sum of positive divisors of N, then a(n+1) = sigma(a(n)) if a(n) is a deficient number, a(n+1) = sigma(a(n))-a(n) if a(n) is a primitive abundant number, a(n+1) = sigma(a(n))-a(n)-m if a(n) is an abundant number with one proper divisor m that is either abundant or perfect, and so forth. LINKS FORMULA a(n+4) = a(n). EXAMPLE a(1) = 34, a(2) = sigma(34) = 54, a(3) = sigma(54)-18-6 = 42, a(4) = sigma(42)-42-6 = 48, a(5) = sigma(48)-48-24-12-6 = 34 = a(1), ... CROSSREFS Cf. A125310, A187793, A274338, A274339, A274340, A274549. Sequence in context: A092888 A217768 A217704 * A305061 A051969 A241520 Adjacent sequences:  A274377 A274378 A274379 * A274381 A274382 A274383 KEYWORD nonn,easy AUTHOR Timothy L. Tiffin, Jun 22 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 19 22:32 EDT 2019. Contains 323411 sequences. (Running on oeis4.)