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Template:Sequence of the Day for April 27

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Intended for: April 27, 2013

Timetable

  • First draft entered by Alonso del Arte on March 19, 2012
  • Draft reviewed by Daniel Forgues on April 26, 2012
  • Draft to be approved by March 27, 2013
Yesterday's SOTD * Tomorrow's SOTD

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A024816: Antisigma (n):
x̅σ (n) :=
n

i  = 1

in
i = tn  −  σ (n)
, for
n   ≥   1
.
{ 0, 0, 2, 3, 9, 9, 20, 21, 32, 37, ... }
For primes
p
,
x̅σ (  p) = tp  − 1  −  1 =
p  (  p  − 1)
2
 −  1
, where
tp  − 1
is the
(  p  −  1)
 -th triangular number. Compare with Euler's cototient function
x̅φ (n)
.