21831621 has 16 divisors (see below), whose sum is σ = 35224704. Its totient is φ = 11741184.

The previous prime is 21831617. The next prime is 21831631. The reversal of 21831621 is 12613812.

It is not a de Polignac number, because 21831621 - 2² = 21831617 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21831591 and 21831600.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21831631) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 30220 + ... + 30933.

It is an arithmetic number, because the mean of its divisors is an integer number (2201544).

Almost surely, 2^21831621 is an apocalyptic number.

21831621 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21831621 is a deficient number, since it is larger than the sum of its proper divisors (13393083).

21831621 is a wasteful number, since it uses less digits than its factorization.

21831621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61180.

The product of its digits is 576, while the sum is 24.

The square root of 21831621 is about 4672.4320219774. The cubic root of 21831621 is about 279.4872461093.

It can be divided in two parts, 21 and 831621, that multiplied together give a square (17464041 = 4179²).

The spelling of 21831621 in words is "twenty-one million, eight hundred thirty-one thousand, six hundred twenty-one".