http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Number-Theoretic-Functions.html
Function: void mpz_fib_ui (mpz_t fn , unsigned long int n ) ¶ Function: void mpz_fib2_ui (mpz_t fn , mpz_t fnsub1 , unsigned long int n ) ¶ mpz_fib_ui sets fn to F[n] , the n th Fibonacci
number. mpz_fib2_ui sets fn to F[n] , and fnsub1 to F[n-1] . These functions are designed for calculating isolated Fibonacci numbers.