86

Number
$86$ (eighty-six) is:
 * $2 \times 43$


 * The $28$th semiprime:
 * $86 = 2 \times 43$


 * The $10$th nontotient after $14, 26, 34, 38, 50, 62, 68, 74, 76$:
 * $\nexists m \in \Z_{>0}: \phi \left({m}\right) = 86$
 * where $\phi \left({m}\right)$ denotes the Euler $\phi$ function


 * The $7$th noncototient after $10, 26, 34, 50, 52, 58$:
 * $\nexists m \in \Z_{>0}: m - \phi \left({m}\right) = 86$
 * where $\phi \left({m}\right)$ denotes the Euler $\phi$ function


 * The $16$th happy number after $1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82$:
 * $86 \to 8^2 + 6^2 = 64 + 36 = 100 \to 1^2 + 0^2 + 0^2 = 1$


 * Believed to be the largest $n$ such that $2^n$ contains no zero in its decimal representation:
 * $2^{86} = 147 \, 573 \, 952 \, 589 \, 676 \, 412 \, 928$

Also see

 * Powers of 2 with no Zero in Decimal Representation