21253621 has 8 divisors (see below), whose sum is σ = 23053464. Its totient is φ = 19514880.

The previous prime is 21253613. The next prime is 21253627. The reversal of 21253621 is 12635212.

It can be written as a sum of positive squares in 4 ways, for example, as 1521 + 21252100 = 39^2 + 4610^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21253621 - 2³ = 21253613 is a prime.

It is a super-2 number, since 2×21253621² = 903432811223282, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21253592 and 21253601.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21253627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14550 + ... + 15943.

It is an arithmetic number, because the mean of its divisors is an integer number (2881683).

Almost surely, 2^21253621 is an apocalyptic number.

It is an amenable number.

21253621 is a deficient number, since it is larger than the sum of its proper divisors (1799843).

21253621 is a wasteful number, since it uses less digits than its factorization.

21253621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30551.

The product of its digits is 720, while the sum is 22.

The square root of 21253621 is about 4610.1649645105. The cubic root of 21253621 is about 276.9986445736.

Adding to 21253621 its reverse (12635212), we get a palindrome (33888833).

The spelling of 21253621 in words is "twenty-one million, two hundred fifty-three thousand, six hundred twenty-one".