21391525 has 12 divisors (see below), whose sum is σ = 28086372. Its totient is φ = 16106240.

The previous prime is 21391523. The next prime is 21391543. The reversal of 21391525 is 52519312.

It can be written as a sum of positive squares in 6 ways, for example, as 543169 + 20848356 = 737^2 + 4566^2 .

It is not a de Polignac number, because 21391525 - 2¹ = 21391523 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21391493 and 21391502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391523) 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 11 ways as a sum of consecutive naturals, for example, 24742 + ... + 25591.

It is an arithmetic number, because the mean of its divisors is an integer number (2340531).

Almost surely, 2^21391525 is an apocalyptic number.

21391525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21391525 is a deficient number, since it is larger than the sum of its proper divisors (6694847).

21391525 is a wasteful number, since it uses less digits than its factorization.

21391525 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50360 (or 50355 counting only the distinct ones).

The product of its digits is 2700, while the sum is 28.

The square root of 21391525 is about 4625.0972962739. The cubic root of 21391525 is about 277.5964548501.

The spelling of 21391525 in words is "twenty-one million, three hundred ninety-one thousand, five hundred twenty-five".