login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A053248 Second differences of sigma(n) that are negative. 2
1, 4, 10, 9, 11, 30, 10, 20, 40, 32, 16, 65, 13, 42, 82, 46, 12, 96, 26, 82, 106, 46, 18, 143, 57, 70, 114, 88, 40, 214, 26, 66, 136, 88, 120, 244, 30, 60, 160, 171, 47, 256, 36, 150, 266, 96, 40, 286, 88, 176, 226, 124, 12, 24, 342, 170, 230, 222, 94, 34, 443, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..62.

FORMULA

a(n) = A053223(A053229(n))

MAPLE

with (numtheory): f := [seq( sigma(i+2) - sigma(i+1) - (sigma(i+1) - sigma(i)), i=1..200)];

seq(`if`(f[i] < 0, f[i], print( )), i=1..200);

MATHEMATICA

Abs[Select[Differences[DivisorSigma[1, Range[200]], 2], Negative]] (* Harvey P. Dale, Aug 13 2015 *)

CROSSREFS

Cf. A000203, A053223, A053247.

Sequence in context: A073722 A320577 A199805 * A081547 A264272 A264257

Adjacent sequences:  A053245 A053246 A053247 * A053249 A053250 A053251

KEYWORD

nonn

AUTHOR

Asher Auel (asher.auel(AT)reed.edu) Jan 11, 2000

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 February 20 22:51 EST 2019. Contains 320362 sequences. (Running on oeis4.)