21621823 has 2 divisors, whose sum is σ = 21621824. Its totient is φ = 21621822.

The previous prime is 21621793. The next prime is 21621851. The reversal of 21621823 is 32812612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21621823 is a prime.

It is equal to p_1366810 and since 21621823 and 1366810 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21621923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810911 + 10810912.

It is an arithmetic number, because the mean of its divisors is an integer number (10810912).

Almost surely, 2^21621823 is an apocalyptic number.

21621823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621823 is an equidigital number, since it uses as much as digits as its factorization.

21621823 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 25.

The square root of 21621823 is about 4649.9272037313. The cubic root of 21621823 is about 278.5890886271.

The spelling of 21621823 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred twenty-three".