21863121 has 16 divisors (see below), whose sum is σ = 33661824. Its totient is φ = 12363264.

The previous prime is 21863119. The next prime is 21863141. The reversal of 21863121 is 12136812.

It is not a de Polignac number, because 21863121 - 2¹ = 21863119 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21863091 and 21863100.

It is not an unprimeable number, because it can be changed into a prime (21863141) 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 15 ways as a sum of consecutive naturals, for example, 3330 + ... + 7403.

It is an arithmetic number, because the mean of its divisors is an integer number (2103864).

Almost surely, 2^21863121 is an apocalyptic number.

21863121 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21863121 is a deficient number, since it is larger than the sum of its proper divisors (11798703).

21863121 is a wasteful number, since it uses less digits than its factorization.

21863121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10840.

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

The square root of 21863121 is about 4675.8016424994. The cubic root of 21863121 is about 279.6216019503.

Adding to 21863121 its reverse (12136812), we get a palindrome (33999933).

The spelling of 21863121 in words is "twenty-one million, eight hundred sixty-three thousand, one hundred twenty-one".