Extending A075880, how to find n for A001481(n)=x for large x

[Pfoertner, Hugo]

I know that an approximate value of the position in A001481(n)=x can be
computed by the formula by Landau
n ~= K_LR * x / sqrt(ln(x)) with K_LR=0.76422365358922..., the
Landau-Ramanujan constant, which is known to 30010 decimal digits according
to
http://numbers.computation.free.fr/Constants/Miscellaneous/Records.html
but this doesn't help.

Hugo Pfoertner