21553729 has 4 divisors (see below), whose sum is σ = 21577860. Its totient is φ = 21529600.

The previous prime is 21553717. The next prime is 21553787. The reversal of 21553729 is 92735512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9443329 + 12110400 = 3073^2 + 3480^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553729 - 2²³ = 13165121 is a prime.

It is a deceptive number, since it divides R_21553728.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21553694 and 21553703.

It is not an unprimeable number, because it can be changed into a prime (21553789) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10672 + ... + 12529.

It is an arithmetic number, because the mean of its divisors is an integer number (5394465).

Almost surely, 2^21553729 is an apocalyptic number.

It is an amenable number.

21553729 is a deficient number, since it is larger than the sum of its proper divisors (24131).

21553729 is an equidigital number, since it uses as much as digits as its factorization.

21553729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24130.

The product of its digits is 18900, while the sum is 34.

The square root of 21553729 is about 4642.5993796579. The cubic root of 21553729 is about 278.2963258513.

The spelling of 21553729 in words is "twenty-one million, five hundred fifty-three thousand, seven hundred twenty-nine".