21408623 has 2 divisors, whose sum is σ = 21408624. Its totient is φ = 21408622.

The previous prime is 21408613. The next prime is 21408659. The reversal of 21408623 is 32680412.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21408623 is a prime.

It is a super-2 number, since 2×21408623² = 916658277512258, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21408592 and 21408601.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21408613) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10704311 + 10704312.

It is an arithmetic number, because the mean of its divisors is an integer number (10704312).

Almost surely, 2^21408623 is an apocalyptic number.

21408623 is a deficient number, since it is larger than the sum of its proper divisors (1).

21408623 is an equidigital number, since it uses as much as digits as its factorization.

21408623 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2304, while the sum is 26.

The square root of 21408623 is about 4626.9453206192. The cubic root of 21408623 is about 277.6703950387.

The spelling of 21408623 in words is "twenty-one million, four hundred eight thousand, six hundred twenty-three".