21991939 has 2 divisors, whose sum is σ = 21991940. Its totient is φ = 21991938.

The previous prime is 21991919. The next prime is 21991943. The reversal of 21991939 is 93919912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21991939 - 2¹³ = 21983747 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21991895 and 21991904.

It is not a weakly prime, because it can be changed into another prime (21991909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10995969 + 10995970.

It is an arithmetic number, because the mean of its divisors is an integer number (10995970).

Almost surely, 2^21991939 is an apocalyptic number.

21991939 is a deficient number, since it is larger than the sum of its proper divisors (1).

21991939 is an equidigital number, since it uses as much as digits as its factorization.

21991939 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 39366, while the sum is 43.

The square root of 21991939 is about 4689.5563756074. The cubic root of 21991939 is about 280.1697057953.

The spelling of 21991939 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred thirty-nine".