# 37

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## Number

$37$ (**thirty-seven**) is:

- The $12$th prime number, after $2$, $3$, $5$, $7$, $11$, $13$, $17$, $19$, $23$, $29$, $31$

- The $4$th centered hexagonal number after $1$, $7$, $19$:
- $37 = 1 + 6 + 12 + 18 = 4^3 - 3^3$

- The $11$th lucky number:
- $1$, $3$, $7$, $9$, $13$, $15$, $21$, $25$, $31$, $33$, $37$, $\ldots$

- The $4$th emirp after $13$, $17$, $31$

- The $9$th permutable prime after $2$, $3$, $5$, $7$, $11$, $13$, $17$, $31$

- The $2$nd integer which has a reciprocal whose period is $3$:
- $\dfrac 1 {37} = 0 \cdotp \dot 02 \dot 7$

- The $27$th integer $n$ such that $2^n$ contains no zero in its decimal representation:
- $2^{37} = 137 \, 438 \, 953 \, 472$

- The $23$rd positive integer after $2$, $3$, $4$, $7$, $8$, $\ldots$, $26$, $29$, $30$, $31$, $32$, $33$ which cannot be expressed as the sum of distinct pentagonal numbers

- The $4$th prime number of the form $n^2 + 1$ after $2$, $5$, $17$:
- $37 = 6^2 + 1$

- Every positive integer can be expressed as the sum of at most $37$ positive $5$th powers

- The $7$th integer $m$ such that $m! + 1$ (its factorial plus $1$) is prime:
- $0$, $1$, $2$, $3$, $11$, $27$, $37$

- The $4$th prime $p$ after $11$, $23$, $29$ such that the Mersenne number $2^p - 1$ is composite

- The $6$th two-sided prime after $2$, $3$, $5$, $7$, $23$:
- $37$, $3$, $7$ are prime

## Also see

- Period of Reciprocal of 37 has Length 3
- Numbers whose Cyclic Permutations of 3-Digit Multiples are Multiples
- Hilbert-Waring Theorem for $5$th Powers

*Previous ... Next*: Two-Sided Prime

*Previous ... Next*: Pythagorean Prime*Previous ... Next*: Sequence of Indices of Composite Mersenne Numbers

*Previous ... Next*: Prime Number*Previous ... Next*: Emirp*Previous ... Next*: Permutable Prime

*Previous ... Next*: Numbers not Expressible as Sum of Distinct Pentagonal Numbers*Previous ... Next*: Lucky Number

## Sources

- 1986: David Wells:
*Curious and Interesting Numbers*... (previous) ... (next): $37$ - 1997: David Wells:
*Curious and Interesting Numbers*(2nd ed.) ... (previous) ... (next): $37$