OFFSET
1,4
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A072106(2*n-1). - Amiram Eldar, Nov 07 2024
EXAMPLE
For n=105: phi(105) = 48 with 24 odd, 24 even terms in the reduced residue system, of which 9 even terms and (all but 1) odd term is nontotient: a((105+1)/2) = a(53) = 24-1+9 = 32.
For n=21: reduced residue system(21) = Union({1,5,11,13,17,19}, {2,4,8,16,20}) includes 6 odd and 5 even numbers. No even nontotients terms in the reduced residue system(21), so 6-1 = 5 odd terms give all nontotients, so a((21+1)/2) = a(11) = 5.
PROG
(PARI) a(n) = {my(m = 2*n-1); sum(k = 1, m, gcd(m, k) == 1 && !istotient(k)); } \\ Amiram Eldar, Nov 07 2024
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Labos Elemer, Jun 19 2002
STATUS
approved