21949409 has 2 divisors, whose sum is σ = 21949410. Its totient is φ = 21949408.

The previous prime is 21949387. The next prime is 21949453. The reversal of 21949409 is 90494912.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12780625 + 9168784 = 3575^2 + 3028^2 .

It is a cyclic number.

It is not a de Polignac number, because 21949409 - 2²⁰ = 20900833 is a prime.

It is not a weakly prime, because it can be changed into another prime (21949489) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10974704 + 10974705.

It is an arithmetic number, because the mean of its divisors is an integer number (10974705).

Almost surely, 2^21949409 is an apocalyptic number.

It is an amenable number.

21949409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21949409 is an equidigital number, since it uses as much as digits as its factorization.

21949409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 21949409 is about 4685.0196370987. The cubic root of 21949409 is about 279.9889834101.

The spelling of 21949409 in words is "twenty-one million, nine hundred forty-nine thousand, four hundred nine".