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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A066452 Anti-phi(n). 6
1, 1, 2, 1, 4, 1, 4, 4, 3, 2, 8, 3, 7, 7, 9, 2, 8, 5, 10, 10, 8, 6, 19, 6, 12, 9, 9, 8, 22, 9, 12, 12, 15, 10, 31, 9, 11, 14, 24, 13, 23, 9, 24, 17, 16, 10, 35, 15, 23, 25, 20, 12, 40, 17, 34, 21, 18, 14, 37, 17, 24, 25, 41, 20, 39, 14, 31, 34, 33, 18, 42, 16, 32, 37, 41, 18, 44, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,3

COMMENTS

anti-phi(n) = the number of integers < n that are not divisible by any anti-divisor of n.

The old definition given for this sequence was: anti-phi(n) = number of integers <= n that are coprime to the anti-divisors of n. However this does not match the entries.

See A066272 for definition of anti-divisor.

LINKS

Nathaniel Johnston, Table of n, a(n) for n = 2..10000 [This replaces an earlier b-file computed by Diana Mecum]

Jon Perry, Anti-phi function [Broken link]

Jon Perry, The Anti-divisor [Cached copy]

Jon Perry, The Anti-divisor: Even More Anti-Divisors [Cached copy]

EXAMPLE

10 has anti-divisors 3,4,7. The numbers not divisible by any of 3,4,7 and less than 10 are 1,2,5. Therefore anti-phi(10)=3.

MAPLE

# needs antidivisors() as implemented in A066272

A066452 := proc(n)local ad, isad, j, k, totad:ad:=antidivisors(n):totad:=0:for j from 1 to n-1 do isad:=1:for k from 1 to nops(ad) do if(j mod ad[k]=0)then isad:=0:break: fi:od:totad:=totad+isad:od:return totad:end:

seq(A066452(n), n=2..50); # Nathaniel Johnston, Apr 20 2011

PROG

(Python)

def A066452(n):

....return len([x for x in xrange(1, n) if all([x % d  for d in xrange(2, n) if (n % d) and (2*n) % d in [d-1, 0, 1]])]) # Chai Wah Wu, Aug 07 2014

(PARI) antidiv(n) = {my(v = []); for (k=2, n-1, if (abs((n % k) - k/2) < 1, v = concat(v, k)); ); v; }

a(n) = {my(vad = antidiv(n)); my(nbad = 0); for (j=1, n-1, isad = 1; for (k=1, #vad, if ((j % vad[k]) == 0, isad = 0; break); ); nbad += isad; ); nbad; } \\ Michel Marcus, Feb 25 2016

CROSSREFS

Cf. A058838, A066241.

Sequence in context: A243329 A051953 A079277 * A007104 A102627 A296560

Adjacent sequences:  A066449 A066450 A066451 * A066453 A066454 A066455

KEYWORD

nonn,easy

AUTHOR

Jon Perry, Dec 29 2001

EXTENSIONS

Better definition and more terms from Diana L. Mecum, Jul 01 2007

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 20 01:39 EDT 2018. Contains 316378 sequences. (Running on oeis4.)