21634909 has 2 divisors, whose sum is σ = 21634910. Its totient is φ = 21634908.

The previous prime is 21634871. The next prime is 21634913. The reversal of 21634909 is 90943612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16990884 + 4644025 = 4122^2 + 2155^2 .

It is a cyclic number.

It is not a de Polignac number, because 21634909 - 2¹¹ = 21632861 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21634919) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10817454 + 10817455.

It is an arithmetic number, because the mean of its divisors is an integer number (10817455).

Almost surely, 2^21634909 is an apocalyptic number.

It is an amenable number.

21634909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21634909 is an equidigital number, since it uses as much as digits as its factorization.

21634909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 34.

The square root of 21634909 is about 4651.3341096937. The cubic root of 21634909 is about 278.6452800283.

The spelling of 21634909 in words is "twenty-one million, six hundred thirty-four thousand, nine hundred nine".