21350809 has 2 divisors, whose sum is σ = 21350810. Its totient is φ = 21350808.

The previous prime is 21350803. The next prime is 21350839. The reversal of 21350809 is 90805312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19536400 + 1814409 = 4420^2 + 1347^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21350809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21350803) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10675404 + 10675405.

It is an arithmetic number, because the mean of its divisors is an integer number (10675405).

Almost surely, 2^21350809 is an apocalyptic number.

It is an amenable number.

21350809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21350809 is an equidigital number, since it uses as much as digits as its factorization.

21350809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21350809 is about 4620.6935626592. The cubic root of 21350809 is about 277.4202200115.

The spelling of 21350809 in words is "twenty-one million, three hundred fifty thousand, eight hundred nine".