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pete-3.c is one of the nine entries an anonymous "Pete" submitted to Bignum Bakeoff, and the smallest entry that produces a large number. It uses the left shift operator <<, which in the fictional Bignum Bakeoff machine may be defined as $$a \ll b = a \cdot 2^b$$ for nonnegative $$a$$ and $$b$$. (Its behavior is more complex in standard C implementations.)

Presumably to save space, Pete did not use parentheses. Unfortunately, << is left-associative, and $$a \ll b$$ grows much faster relative to $$b$$ than to $$a$$. So the returned value becomes $$9 \cdot (2^9)^{163} \cdot 2^{99} \approx 2.33 \cdot 10^{472}$$, between a centillion and googolding. A large amount of space is therefore wasted on a number smaller than 1 << 1,600. If the operator was instead right-to-left associative, the output would grow at a roughly tetrational rate with respect to the number of 9's.

The full decimal expansion of this number is:

23,292,479,355,228,506,120,629,103,772,205,782,521,188,556,601,365,594,768,126,262,808,438,806,540,095,385,289,219,152,367,764,951,472,483,434,579,932,913,443,405,761,122,010,738,810,864,711,712,947,727,372,583,238,365,228,030,815,708,368,105,772,248,573,097,826,643,896,491,485,324,536,255,232,791,227,961,592,036,609,194,479,127,526,553,544,504,755,505,641,588,760,449,935,355,381,277,623,598,581,929,299,236,167,791,999,017,226,178,068,796,899,131,268,137,948,410,262,725,752,057,313,568,787,813,656,536,514,657,337,239,890,061,615,130,555,787,285,358,522,635,888,992,125,632,724,527,232,536,411,274,866,890,787,299,237,298,176

Its prime factorization is 21,566 × 32.

## Code

int main()
{
return
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 <<
9 << 9 << 9 << 9 << 9 << 9 << 9 << 9 << 99;
}


## Approximations

Notation Lower bound Upper bound
Scientific notation $$2.329\times10^{472}$$ $$2.33\times10^{472}$$
Arrow notation $$42\uparrow291$$ $$218\uparrow202$$
Steinhaus-Moser Notation 204 205
Copy notation 2 3
Taro's multivariable Ackermann function A(3,1566) A(3,1567)
Pound-Star Notation #*((4918))*13 #*((4919))*13
BEAF {42,291} {218,202}
Hyper-E notation E291 E202
Bashicu matrix system (0)(0)(0)(0)(0)(0)(0) (0)(0)(0)(0)(0)(0)(0)
Hyperfactorial array notation 241! 242!
Fast-growing hierarchy $$f_2(1558)$$ $$f_2(1559)$$
Hardy hierarchy $$H_{\omega^2}(1558)$$ $$H_{\omega^2}(1559)$$
Slow-growing hierarchy $$g_{\omega^{\omega^3+\omega+3}+\omega^{\omega^3+\omega+2}}(8)$$