# 44

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## Number

$44$ (**forty-four**) is:

- $2^2 \times 11$

- The $1$st of the $1$st ordered quadruple of consecutive integers that have sigma values which are strictly decreasing:
- $\map \sigma {44} = 84$, $\map \sigma {45} = 78$, $\map \sigma {46} = 72$, $\map \sigma {47} = 48$

- The $5$th subfactorial after $0$, $1$, $2$, $9$:
- $44 = 5! \left({1 - \dfrac 1 {1!} + \dfrac 1 {2!} - \dfrac 1 {3!} + \dfrac 1 {4!} - \dfrac 1 {5!} }\right)$

- The $1$st of the $1$st pair of consecutive integers which both have $6$ divisors:
- $\map \tau {44} = \map \tau {45} = 6$

- The $10$th happy number after $1$, $7$, $10$, $13$, $19$, $23$, $28$, $31$, $32$:
- $44 \to 4^2 + 4^2 = 16 + 16 = 32 \to 3^2 + 2^2 = 9 + 4 = 13 \to 1^2 + 3^2 = 9 + 1 = 10 \to 1^2 + 0^2 = 1$

- The $20$th positive integer which is not the sum of $1$ or more distinct squares:
- $2$, $3$, $6$, $7$, $8$, $11$, $12$, $15$, $18$, $19$, $22$, $23$, $24$, $27$, $28$, $31$, $32$, $33$, $43$, $44$, $\ldots$

- The $27$th positive integer after $2$, $3$, $4$, $7$, $8$, $\ldots$, $26$, $29$, $30$, $31$, $32$, $33$, $37$, $38$, $42$, $43$ which cannot be expressed as the sum of distinct pentagonal numbers.

- The length of the shortest edge of the smallest cuboid whose edges and the diagonals of whose faces are all integers:

- The largest integer $n$ such that the set of integers from $1$ to $n$ can be partitioned into $4$ subsets such that no integer in any of these subsets is the sum of $2$ other integers in the same subset:

- $\set {1, 3, 5, 15, 17, 19, 26, 28, 40, 42, 44}$
- $\set {2, 7, 8, 18, 21, 24, 27, 33, 37, 38, 43}$
- $\set {4, 6, 13, 20, 22, 23, 25, 30, 32, 39, 41}$
- $\set {9, 10, 11, 12, 14, 16, 29, 31, 34, 35, 36}$

## Also see

- Cuboid with Integer Edges and Face Diagonals
- Largest n such that 1 to n can be Partitioned for no Element to be Sum of 2 Elements in Same Set

*Previous ... Next*: Subfactorial*Previous ... Next*: Happy Number

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

*Next*: Sequences of 4 Consecutive Integers with Falling Sigma*Next*: Pairs of Consecutive Integers with 6 Divisors

## Sources

- 1986: David Wells:
*Curious and Interesting Numbers*... (previous) ... (next): $44$ - 1997: David Wells:
*Curious and Interesting Numbers*(2nd ed.) ... (previous) ... (next): $44$