21123261 has 12 divisors (see below), whose sum is σ = 31641792. Its totient is φ = 14082012.

The previous prime is 21123211. The next prime is 21123287. The reversal of 21123261 is 16232112.

It is not a de Polignac number, because 21123261 - 2⁷ = 21123133 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 43221 + ... + 43706.

It is an arithmetic number, because the mean of its divisors is an integer number (2636816).

Almost surely, 2^21123261 is an apocalyptic number.

It is an amenable number.

21123261 is a deficient number, since it is larger than the sum of its proper divisors (10518531).

21123261 is an frugal number, since it uses more digits than its factorization.

21123261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86942 (or 86930 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21123261 is about 4596.0048955588. The cubic root of 21123261 is about 276.4311550404.

Adding to 21123261 its reverse (16232112), we get a palindrome (37355373).

The spelling of 21123261 in words is "twenty-one million, one hundred twenty-three thousand, two hundred sixty-one".