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Fifty-fives is equal to $$5 \lfloor 10^{50} / 9\rfloor$$, or 50 copies of 5:[1]

55,555,555,555,555,555,555,555,555,555,555,555,555,555,555,555,555
can be represented hypermathematically with interior superscription as $$5^{48}5$$.

It's also equal to $$\frac{5}{9}\times(10^{50}-1)$$, and its prime factorization is 5 × 11 × 41 × 251 × 271 × 5,051 × 9,091 × 21,401 × 25,601 × 182,521,213,001 × 78,875,943,472,201.

## Approximations

Notation Lower bound Upper bound
Scientific notation $$5.555\times10^{49}$$ $$5.556\times10^{49}$$
Arrow notation $$118\uparrow24$$ $$82\uparrow26$$
Steinhaus-Moser Notation 32[3] 33[3]
Copy notation 5[50]
Taro's multivariable Ackermann function A(3,162) A(3,163)
Pound-Star Notation #*(10,2,4,3,1)*8 #*(6,3,1,2,5)*7
BEAF {118,24} {82,26}
Hyper-E notation 5E49 6E49
Bashicu matrix system (0)(0)(0)(0)[1285] (0)(0)(0)(0)[1286]
Hyperfactorial array notation 41! 42!
Fast-growing hierarchy $$f_2(157)$$ $$f_2(158)$$
Hardy hierarchy $$H_{\omega^2}(157)$$ $$H_{\omega^2}(158)$$
Slow-growing hierarchy $$g_{\omega^{\omega+18}2}(20)$$ $$g_{\omega^{\omega+3}10}(30)$$

## Sources

1. Halm, Michael Joseph. neologisms. Archived from the original on 2014-02-19. Retrieved 2018-02-26.