21020819 has 2 divisors, whose sum is σ = 21020820. Its totient is φ = 21020818.

The previous prime is 21020803. The next prime is 21020837. The reversal of 21020819 is 91802012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21020819 - 2⁴ = 21020803 is a prime.

It is a super-2 number, since 2×21020819² = 883749662861522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a junction number, because it is equal to n+sod(n) for n = 21020794 and 21020803.

It is not a weakly prime, because it can be changed into another prime (21020849) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510409 + 10510410.

It is an arithmetic number, because the mean of its divisors is an integer number (10510410).

Almost surely, 2^21020819 is an apocalyptic number.

21020819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020819 is an equidigital number, since it uses as much as digits as its factorization.

21020819 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 21020819 is about 4584.8466713730. The cubic root of 21020819 is about 275.9835590221.

The spelling of 21020819 in words is "twenty-one million, twenty thousand, eight hundred nineteen".