21809101 has 2 divisors, whose sum is σ = 21809102. Its totient is φ = 21809100.

The previous prime is 21809087. The next prime is 21809111. The reversal of 21809101 is 10190812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18922500 + 2886601 = 4350^2 + 1699^2 .

It is a cyclic number.

It is not a de Polignac number, because 21809101 - 2⁵ = 21809069 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21809111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904550 + 10904551.

It is an arithmetic number, because the mean of its divisors is an integer number (10904551).

Almost surely, 2^21809101 is an apocalyptic number.

It is an amenable number.

21809101 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809101 is an equidigital number, since it uses as much as digits as its factorization.

21809101 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 22.

The square root of 21809101 is about 4670.0215202930. The cubic root of 21809101 is about 279.3911131012.

Adding to 21809101 its reverse (10190812), we get a palindrome (31999913).

The spelling of 21809101 in words is "twenty-one million, eight hundred nine thousand, one hundred one".