21521249 has 2 divisors, whose sum is σ = 21521250. Its totient is φ = 21521248.

The previous prime is 21521183. The next prime is 21521251. The reversal of 21521249 is 94212512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15054400 + 6466849 = 3880^2 + 2543^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521249 is a prime.

Together with 21521251, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21521299) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760624 + 10760625.

It is an arithmetic number, because the mean of its divisors is an integer number (10760625).

Almost surely, 2^21521249 is an apocalyptic number.

It is an amenable number.

21521249 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521249 is an equidigital number, since it uses as much as digits as its factorization.

21521249 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 26.

The square root of 21521249 is about 4639.1000204781. The cubic root of 21521249 is about 278.1564643778.

It can be divided in two parts, 2 and 1521249, that added together give a palindrome (1521251).

The spelling of 21521249 in words is "twenty-one million, five hundred twenty-one thousand, two hundred forty-nine".