(33s) OEIS A2516: EARLIEST SEQUENCE WITH A(A(N)) = 2N

[John Keith]

I copied and pasted your code to EMU48 and with an input of 7 I got

[ 2 4 3 8 10 6 15 ].

Could there be a typo in your code?

As far as speed is concerned, accumulating numbers on the stack and storing them in a list or array at the end is significantly faster than using GET and PUT on an existing array. Also stack operations such as PICK and ROLL are very fast, sometimes even faster than list processing commands on later calculators.