Harper.c is a number entered in the Bignum Bakeoff contest.[1], by Russel Harper[2].

The upper bound is E(2**(2**(10**8+2))) and the higher bound E(2**(2**(10**8+3))). Here x**y denotes x to the power of y and E(x) is 2 tetrated to the xth.


The C program is the following:

#define I int
#define w while
#define r return
I l(I x){I y=x;w(y--)x*=x;r x;}
I k(I x,I y){w(y--)x*=k(x,y)*l(x);r x;}
I j(I x,I y){w(y--)x*=j(x,y)*k(x,y);r x;}
I i(I x,I y){w(y--)x*=i(x,y)*j(x,y);r x;}
I h(I x,I y){w(y--)x*=h(x,y)*i(x,y);r x;}
I g(I x,I y){w(y--)x*=g(x,y)*h(x,y);r x;}
I f(I x,I y){w(y--)x*=f(x,y)*g(x,y);r x;}
I e(I x,I y){w(y--)x*=e(x,y)*f(x,y);r x;}
I d(I x,I y){w(y--)x*=d(x,y)*e(x,y);r x;}
I c(I x,I y){w(y--)x*=c(x,y)*d(x,y);r x;}
I b(I x,I y){w(y--)x*=b(x,y)*c(x,y);r x;}
I a(I x,I y){w(y--)x*=a(x,y)*b(x,y);r x;}
I main(void){r a(9<<99999999,9<<99999999);}