21621923 has 2 divisors, whose sum is σ = 21621924. Its totient is φ = 21621922.

The previous prime is 21621881. The next prime is 21621931. The reversal of 21621923 is 32912612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21621923 - 2¹⁶ = 21556387 is a prime.

It is a Sophie Germain prime.

It is a junction number, because it is equal to n+sod(n) for n = 21621892 and 21621901.

It is not a weakly prime, because it can be changed into another prime (21621823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810961 + 10810962.

It is an arithmetic number, because the mean of its divisors is an integer number (10810962).

Almost surely, 2^21621923 is an apocalyptic number.

21621923 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621923 is an equidigital number, since it uses as much as digits as its factorization.

21621923 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1296, while the sum is 26.

The square root of 21621923 is about 4649.9379565753. The cubic root of 21621923 is about 278.5895181140.

The spelling of 21621923 in words is "twenty-one million, six hundred twenty-one thousand, nine hundred twenty-three".