Dr. Ir. (Achmed) Soekarno, volcano

 Volcano

serial # and letters
6 digit serial # and two capital Block letters, or one capital and one lower case letter

without serial #, 2 capital Block letters only

For this note (P-17a) the following "Huisman Table" for fixed relation between serial # and Block letters is applicable:

The first number of the serial # of this note is "5". So the only possible first Block letter are either A, B or C.
This note has the number 528416 Cx

Conclusion: It could be genuine.