34

Number
$34$ (thirty-four) is:
 * $2 \times 17$


 * The $2$nd non-square positive integer which cannot be expressed as the sum of a square and a prime:
 * $10$, $34$, $\ldots$


 * The $3$rd nontotient after $14$, $26$:
 * $\nexists m \in \Z_{>0}: \map \phi m = 34$
 * where $\map \phi m$ denotes the Euler $\phi$ function


 * The $3$rd noncototient after $10$, $26$:
 * $\nexists m \in \Z_{>0}: m - \map \phi m = 34$
 * where $\map \phi m$ denotes the Euler $\phi$ function


 * The smallest positive integer which can be expressed as the sum of $2$ distinct lucky numbers in $4$ different ways:
 * $34 = 1 + 33 = 3 + 31 = 9 + 25 = 13 + 21$


 * The smallest positive integer which can be expressed as the sum of $2$ odd primes in $4$ ways:
 * $34 = 31 + 3 = 29 + 7 = 23 + 11 = 17 + 17$


 * The $4$th positive integer which cannot be expressed as the sum of a square and a prime:
 * $1$, $10$, $25$, $34$, $\ldots$


 * The $4$th heptagonal number after $1$, $7$, $18$:
 * $34 = 1 + 7 + 11 + 16 = \dfrac {4 \paren {5 \times 4 - 3} } 2$


 * The magic constant of a magic square of order $4$, after $1$, $(5)$, $15$:
 * $\ds 34 = \frac 1 4 \sum_{k \mathop = 1}^{4^2} k = \frac {4 \paren {4^2 + 1} } 2$


 * The $9$th Fibonacci number, after $1$, $1$, $2$, $3$, $5$, $8$, $13$, $21$:
 * $34 = 13 + 21$


 * The $12$th semiprime after $4$, $6$, $9$, $10$, $14$, $15$, $21$, $22$, $25$, $26$, $33$:
 * $34 = 2 \times 17$


 * The $24$th integer $n$ such that $2^n$ contains no zero in its decimal representation:
 * $2^{34} = 17 \, 179 \, 869 \, 184$

Also see

 * Sum of 2 Lucky Numbers in 4 Ways