21251545 has 24 divisors (see below), whose sum is σ = 29942784. Its totient is φ = 14436576.

The previous prime is 21251543. The next prime is 21251597. The reversal of 21251545 is 54515212.

It is not a de Polignac number, because 21251545 - 2¹ = 21251543 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21251543) 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 23 ways as a sum of consecutive naturals, for example, 30774 + ... + 31456.

It is an arithmetic number, because the mean of its divisors is an integer number (1247616).

Almost surely, 2^21251545 is an apocalyptic number.

It is an amenable number.

21251545 is a deficient number, since it is larger than the sum of its proper divisors (8691239).

21251545 is a wasteful number, since it uses less digits than its factorization.

21251545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 829 (or 822 counting only the distinct ones).

The product of its digits is 2000, while the sum is 25.

The square root of 21251545 is about 4609.9398043792. The cubic root of 21251545 is about 276.9896254374.

Adding to 21251545 its reverse (54515212), we get a palindrome (75766757).

The spelling of 21251545 in words is "twenty-one million, two hundred fifty-one thousand, five hundred forty-five".