OFFSET
1,4
FORMULA
a(n) = Sum_{k=1..n} [mu(k) = mu(n-k+1)], where mu is the Möbius function (A008683) and [ ] is the Iverson bracket.
EXAMPLE
a(6) = 4; for n=6 and k=1,2,5,6 we have mu(1) = 1 = mu(6-1+1), mu(2) = -1 = mu(6-2+1), mu(5) = -1 = mu(6-5+1), mu(6) = 1 = mu(6-6+1).
MATHEMATICA
Table[Sum[KroneckerDelta[MoebiusMu[n - k + 1], MoebiusMu[k]], {k, n}], {n, 100}]
PROG
(PARI) a(n) = sum(k=1, n, moebius(k) == moebius(n-k+1)); \\ Michel Marcus, May 04 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, May 04 2023
STATUS
approved