Template:Sequence of the Day for April 27

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 i∤n i = tn  −  σ (n)

, for

n   ≥   1

.

{ 0, 0, 2, 3, 9, 9, 20, 21, 32, 37, ... }

For primes

p

,

x̅σ (  p) = t p  − 1  −  1 = p  (  p  − 1) 2  −  1

, where

t p  − 1

is the

(  p  −  1)

 -th triangular number. Compare with Euler's cototient function

x̅φ (n)

.