21521413 has 2 divisors, whose sum is σ = 21521414. Its totient is φ = 21521412.

The previous prime is 21521389. The next prime is 21521419. The reversal of 21521413 is 31412512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17960644 + 3560769 = 4238^2 + 1887^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21521419) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760706 + 10760707.

It is an arithmetic number, because the mean of its divisors is an integer number (10760707).

Almost surely, 2^21521413 is an apocalyptic number.

It is an amenable number.

21521413 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521413 is an equidigital number, since it uses as much as digits as its factorization.

21521413 is an evil number, because the sum of its binary digits is even.

The product of its digits is 240, while the sum is 19.

The square root of 21521413 is about 4639.1176962867. The cubic root of 21521413 is about 278.1571709283.

Adding to 21521413 its reverse (31412512), we get a palindrome (52933925).

The spelling of 21521413 in words is "twenty-one million, five hundred twenty-one thousand, four hundred thirteen".