21398751 has 12 divisors (see below), whose sum is σ = 33719400. Its totient is φ = 12968880.

The previous prime is 21398747. The next prime is 21398753. The reversal of 21398751 is 15789312.

It is not a de Polignac number, because 21398751 - 2² = 21398747 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21398753) 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 11 ways as a sum of consecutive naturals, for example, 107976 + ... + 108173.

It is an arithmetic number, because the mean of its divisors is an integer number (2809950).

Almost surely, 2^21398751 is an apocalyptic number.

21398751 is a deficient number, since it is larger than the sum of its proper divisors (12320649).

21398751 is a wasteful number, since it uses less digits than its factorization.

21398751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216166 (or 216163 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21398751 is about 4625.8784030711. The cubic root of 21398751 is about 277.6277084449.

The spelling of 21398751 in words is "twenty-one million, three hundred ninety-eight thousand, seven hundred fifty-one".