47

Number
$47$ (forty-seven) is:


 * The $15$th prime number, after $2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43$


 * The $8$th Lucas number after $(2), 1, 3, 4, 7, 11, 18, 29$:
 * $47 = 18 + 29$


 * The $4$th of $29$ primes of the form $2 x^2 + 29$:
 * $2 \times 3^2 + 29 = 47$