21252561 has 24 divisors (see below), whose sum is σ = 31460352. Its totient is φ = 12751200.

The previous prime is 21252551. The next prime is 21252571. The reversal of 21252561 is 16525212.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21252551) and next prime (21252571).

It is not a de Polignac number, because 21252561 - 2⁷ = 21252433 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21252551) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 45871 + ... + 46331.

It is an arithmetic number, because the mean of its divisors is an integer number (1310848).

Almost surely, 2^21252561 is an apocalyptic number.

It is an amenable number.

21252561 is a deficient number, since it is larger than the sum of its proper divisors (10207791).

21252561 is a wasteful number, since it uses less digits than its factorization.

21252561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 613 (or 602 counting only the distinct ones).

The product of its digits is 1200, while the sum is 24.

The square root of 21252561 is about 4610.0499997289. The cubic root of 21252561 is about 276.9940395004.

Adding to 21252561 its reverse (16525212), we get a palindrome (37777773).

The spelling of 21252561 in words is "twenty-one million, two hundred fifty-two thousand, five hundred sixty-one".