21399261 has 16 divisors (see below), whose sum is σ = 30897216. Its totient is φ = 13095936.

The previous prime is 21399239. The next prime is 21399299. The reversal of 21399261 is 16299312.

It is not a de Polignac number, because 21399261 - 2⁵ = 21399229 is a prime.

It is a super-2 number, since 2×21399261² = 915856742692242, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21399221) 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, 6106 + ... + 8948.

It is an arithmetic number, because the mean of its divisors is an integer number (1931076).

Almost surely, 2^21399261 is an apocalyptic number.

It is an amenable number.

21399261 is a deficient number, since it is larger than the sum of its proper divisors (9497955).

21399261 is a wasteful number, since it uses less digits than its factorization.

21399261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3052.

The product of its digits is 5832, while the sum is 33.

The square root of 21399261 is about 4625.9335274083. The cubic root of 21399261 is about 277.6299140099.

The spelling of 21399261 in words is "twenty-one million, three hundred ninety-nine thousand, two hundred sixty-one".