197

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Number

$197$ (one hundred and ninety-seven) is:

The $45$th prime number

The $6$th prime number of the form $n^2 + 1$ after $2$, $5$, $17$, $37$, $101$:

$197 = 14^2 + 1$

The $7$th Keith number after $14$, $19$, $28$, $47$, $61$, $75$:

$1$, $9$, $7$, $17$, $33$, $57$, $107$, $197$, $\ldots$

The smaller of the $15$th pair of twin primes, with $199$

The $20$th left-truncatable prime after $2$, $3$, $5$, $7$, $13$, $17$, $23$, $37$, $43$, $47$, $53$, $67$, $73$, $83$, $97$, $113$, $137$, $167$, $173$

Also see

• Previous  ... Next: Keith Number

• Previous  ... Next: Primes of Form n^2 + 1

• Previous  ... Next: Left-Truncatable Prime

• Previous  ... Next: Prime Number
• Previous  ... Next: Twin Primes