• 23 can be written using four 4's:

• Deleting all the even digits from 2^{23} = 8388608 we obtain a prime (3).

23 has 2 divisors, whose sum is σ = 24. Its totient is φ = 22.

The previous prime is 19. The next prime is 29. The reversal of 23 is 32.

Added to its reverse (32) it gives a triangular number (55 = T_{10}).

It is a happy number.

23 is nontrivially palindromic in base 3.

23 is an esthetic number in base 3, base 5, base 7, base 10 and base 11, because in such bases its adjacent digits differ by 1.

It is a m-pointer prime, because the next prime (29) can be obtained adding 23 to its product of digits (6).

It is a weak prime.

23 is a truncatable prime.

It is a cyclic number.

It is not a de Polignac number, because 23 - 2^{2} = 19 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a magnanimous number.

It is an alternating number because its digits alternate between even and odd.

It is a Kynea number, being equal to (2^{2} + 1)^{2} - 2.

It is a lonely number, since its distance to closest prime (19) sets a new record.

23 is an undulating number in base 3.

23 is a modest number, since divided by 3 gives 2 as remainder.

It is a plaindrome in base 4, base 6, base 8, base 9, base 10, base 12, base 13, base 14, base 15 and base 16.

It is a nialpdrome in base 5, base 7 and base 11.

It is a congruent number.

It is a panconsummate number.

Being equal to 3×2^{3}-1, it is a Woodall number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 11 + 12.

It is an arithmetic number, because the mean of its divisors is an integer number (12).

23 is a deficient number, since it is larger than the sum of its proper divisors (1).

23 is an equidigital number, since it uses as much as digits as its factorization.

It is an anagram of its base 7 representation: 23 = (32)_{7}.

23 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6, while the sum is 5.

The square root of 23 is about 4.7958315233. The cubic root of 23 is about 2.8438669799.

Adding to 23 its reverse (32), we get a palindrome (55).

The spelling of 23 in words is "twenty-three", and thus it is an aban number, an iban number, an oban number, and an uban number.

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