login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A274849 Isolated deficient numbers. 5
19, 29, 41, 55, 71, 79, 89, 101, 103, 113, 139, 161, 175, 197, 199, 209, 221, 223, 259, 271, 281, 305, 307, 319, 341, 349, 351, 353, 365, 367, 379, 391, 401, 415, 439, 449, 461, 463, 475, 491, 497, 499, 521, 533, 545, 551, 559, 571, 581, 607, 617, 619, 641, 643, 649, 679, 701, 703, 727, 737, 739, 749 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Deficient numbers a(n) for which a(n)-1 and a(n)+1 are not deficient.  In most instances, both a(n)-1 and a(n)+1 will be abundant numbers; in a few instances, one will be abundant while the other one is perfect.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000 (First 413 terms from Timothy L. Tiffin)

EXAMPLE

19 is between two abundant numbers (18 and 20), while 29 is between a perfect number (28) and an abundant number (30).

MATHEMATICA

Select[Range@ 750, Boole@ Map[DivisorSigma[1, #] < 2 # &, # + {-1, 0, 1}] == {0, 1, 0} &] (* Michael De Vlieger, Aug 26 2016 *)

SequencePosition[Table[If[DivisorSigma[1, n]<2n, 1, 0], {n, 800}], {0, 1, 0}][[All, 1]]+1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 21 2017 *)

CROSSREFS

Subsequence of A005100.

Sequence in context: A158846 A157026 A240724 * A276049 A108183 A157483

Adjacent sequences:  A274846 A274847 A274848 * A274850 A274851 A274852

KEYWORD

nonn

AUTHOR

Timothy L. Tiffin, Jul 08 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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 11:49 EDT 2020. Contains 333083 sequences. (Running on oeis4.)