21649621 has 6 divisors (see below), whose sum is σ = 25184310. Its totient is φ = 18556776.

The previous prime is 21649609. The next prime is 21649627. The reversal of 21649621 is 12694612.

It can be written as a sum of positive squares in only one way, i.e., 16313521 + 5336100 = 4039^2 + 2310^2 .

It is not a de Polignac number, because 21649621 - 2¹¹ = 21647573 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21649627) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 220866 + ... + 220963.

It is an arithmetic number, because the mean of its divisors is an integer number (4197385).

Almost surely, 2^21649621 is an apocalyptic number.

It is an amenable number.

21649621 is a deficient number, since it is larger than the sum of its proper divisors (3534689).

21649621 is an equidigital number, since it uses as much as digits as its factorization.

21649621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 441843 (or 441836 counting only the distinct ones).

The product of its digits is 5184, while the sum is 31.

The square root of 21649621 is about 4652.9153226767. The cubic root of 21649621 is about 278.7084264381.

The spelling of 21649621 in words is "twenty-one million, six hundred forty-nine thousand, six hundred twenty-one".