OFFSET
1,2
FORMULA
a(n) = phi(2*n-1) - A072454(n). [Corrected by Sean A. Irvine, Oct 04 2024]
EXAMPLE
n=31: reduced residue system[31]={1,...,30} with 15 odd and 15 even numbers. From odd ones only term=1 is totient, while from 15 even terms, 2 ones,{14,26},are nontotients so 13 ones are totients. All totients count 1+13=14, thus a([31+1]/2)=a(16)=14.
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jun 19 2002
STATUS
approved