21252591 has 16 divisors (see below), whose sum is σ = 31564800. Its totient is φ = 14132664.

The previous prime is 21252589. The next prime is 21252593. The reversal of 21252591 is 19525212.

21252591 is a `hidden beast` number, since 21 + 2 + 52 + 591 = 666.

It is an interprime number because it is at equal distance from previous prime (21252589) and next prime (21252593).

It is not a de Polignac number, because 21252591 - 2¹ = 21252589 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21252593) 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, 14050 + ... + 15488.

It is an arithmetic number, because the mean of its divisors is an integer number (1972800).

Almost surely, 2^21252591 is an apocalyptic number.

21252591 is a deficient number, since it is larger than the sum of its proper divisors (10312209).

21252591 is a wasteful number, since it uses less digits than its factorization.

21252591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1995 (or 1989 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 21252591 is about 4610.0532534885. The cubic root of 21252591 is about 276.9941698348.

The spelling of 21252591 in words is "twenty-one million, two hundred fifty-two thousand, five hundred ninety-one".