# 205

Previous  ... Next

## Number

$205$ (two hundred and five) is:

$5 \times 41$

The $4$th positive integer after $200$, $202$, $204$ that cannot be made into a prime number by changing just $1$ digit

The $10$th positive integer after $50$, $65$, $85$, $125$, $130$, $145$, $170$, $185$, $200$ which can be expressed as the sum of two square numbers in two or more different ways:
$205 = 14^2 + 3^2 = 13^2 + 6^2$

The $13$th integer after $7$, $13$, $19$, $35$, $38$, $41$, $57$, $65$, $70$, $125$, $130$, $190$ the decimal representation of whose square can be split into two parts which are each themselves square:
$205^2 = 42 \, 025$; $4 = 2^2$, $2025 = 45^2$

The $40$th lucky number:
$1$, $3$, $7$, $9$, $13$, $15$, $21$, $\ldots$, $163$, $169$, $171$, $189$, $193$, $195$, $201$, $205$, $\ldots$

The number of pairs of twin primes less than $10 \, 000$