Smallest Penholodigital Square
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Theorem
The smallest penholodigital square number is:
- $11 \, 826^2 = 139 \, 854 \, 276$
Proof
Let $n$ be the smallest positive integer whose square is penholodigital.
First it is noted that the smallest penholodigital number is $123 \, 456 \, 789$.
Hence any square penholodigital number must be at least as large as that.
Thus we can can say that:
- $n \ge \ceiling {\sqrt {123 \, 456 \, 789} } = 11 \, 112$
where $\ceiling {\, \cdot \,}$ denotes the ceiling function.
It remains to be demonstrated that no positive integer between $11 \, 112$ and $11 \, 826$ has a penholodigital square.
This theorem requires a proof. In particular: This is over $700$ numbers. The task can be filtered by, for example, disregarding all $n$ ending in $1$ and $9$ because their squares will both begin and end in $1$ at this low range of the $10000$s, and of course all $n$ ending in $0$ because their squares will end in $0$. You can help $\mathsf{Pr} \infty \mathsf{fWiki}$ by crafting such a proof. To discuss this page in more detail, feel free to use the talk page. When this work has been completed, you may remove this instance of {{ProofWanted}} from the code.If you would welcome a second opinion as to whether your work is correct, add a call to {{Proofread}} the page. |
Historical Note
$139 \, 854 \, 276$ was remarked upon by John Hill in his $1716$ work Arithmetick, Both in the Theory and Practice, where he stated:
- This number $139854276$ is a very remarkable Number: First, It's a Square Number; Secondly it contains $9$ Places, and they are $9$ Digits, and I think there is not another that does.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $11,826$
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $139,854,276$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $11,826$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $139,854,276$