205

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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 number of pairs of twin primes less than $10^4$

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:

$1$, $3$, $7$, $9$, $13$, $15$, $21$, $\ldots$, $163$, $169$, $171$, $189$, $193$, $195$, $201$, $205$, $\ldots$

Also see

• Integer Greater than 205 is Sum of Distinct Primes of form 6 n + 1

• Previous  ... Next: Number of Twin Primes less than Powers of 10
• Previous  ... Next: Squares whose Digits can be Separated into 2 other Squares
• Previous  ... Next: Sum of 2 Squares in 2 Distinct Ways
• Previous  ... Next: Lucky Number
• Previous  ... Next: Numbers that cannot be made Prime by changing 1 Digit

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $205$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $205$