21393951 has 16 divisors (see below), whose sum is σ = 29008896. Its totient is φ = 14023296.

The previous prime is 21393949. The next prime is 21393959. The reversal of 21393951 is 15939312.

It is not a de Polignac number, because 21393951 - 2¹ = 21393949 is a prime.

It is a super-2 number, since 2×21393951² = 915402278780802, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21393959) 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, 75456 + ... + 75738.

It is an arithmetic number, because the mean of its divisors is an integer number (1813056).

Almost surely, 2^21393951 is an apocalyptic number.

21393951 is a deficient number, since it is larger than the sum of its proper divisors (7614945).

21393951 is a wasteful number, since it uses less digits than its factorization.

21393951 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 622.

The product of its digits is 7290, while the sum is 33.

The square root of 21393951 is about 4625.3595535915. The cubic root of 21393951 is about 277.6069484692.

The spelling of 21393951 in words is "twenty-one million, three hundred ninety-three thousand, nine hundred fifty-one".