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 range(1, n) if all([x % d for d in range(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
KEYWORD
nonn,easy
AUTHOR
Jon Perry, Dec 29 2001
EXTENSIONS
Better definition and more terms from Diana L. Mecum, Jul 01 2007
STATUS
approved