21881819 has 2 divisors, whose sum is σ = 21881820. Its totient is φ = 21881818.

The previous prime is 21881801. The next prime is 21881831. The reversal of 21881819 is 91818812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21881819 is a prime.

It is a super-2 number, since 2×21881819² = 957628005497522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21881219) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10940909 + 10940910.

It is an arithmetic number, because the mean of its divisors is an integer number (10940910).

Almost surely, 2^21881819 is an apocalyptic number.

21881819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21881819 is an equidigital number, since it uses as much as digits as its factorization.

21881819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9216, while the sum is 38.

The square root of 21881819 is about 4677.8006584291. The cubic root of 21881819 is about 279.7012928437.

The spelling of 21881819 in words is "twenty-one million, eight hundred eighty-one thousand, eight hundred nineteen".