21553949 has 2 divisors, whose sum is σ = 21553950. Its totient is φ = 21553948.

The previous prime is 21553933. The next prime is 21553951. The reversal of 21553949 is 94935512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17724100 + 3829849 = 4210^2 + 1957^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553949 - 2⁴ = 21553933 is a prime.

It is a Sophie Germain prime.

Together with 21553951, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21553919) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776974 + 10776975.

It is an arithmetic number, because the mean of its divisors is an integer number (10776975).

Almost surely, 2^21553949 is an apocalyptic number.

It is an amenable number.

21553949 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553949 is an equidigital number, since it uses as much as digits as its factorization.

21553949 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48600, while the sum is 38.

The square root of 21553949 is about 4642.6230732206. The cubic root of 21553949 is about 278.2972727096.

The spelling of 21553949 in words is "twenty-one million, five hundred fifty-three thousand, nine hundred forty-nine".