OFFSET
0,4
FORMULA
PROG
(PARI) a(n) = sum(k=0, n, if (k%2, eulerphi(n-k+1))); \\ Michel Marcus, Jun 12 2024
(Python)
def A106481(n): return A002088(n+1)-A049690(n+1>>1) if n&1 else A049690(n>>1) # Chai Wah Wu, Aug 04 2024
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, May 03 2005
STATUS
approved