21115421 has 2 divisors, whose sum is σ = 21115422. Its totient is φ = 21115420.

The previous prime is 21115417. The next prime is 21115427. The reversal of 21115421 is 12451112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14668900 + 6446521 = 3830^2 + 2539^2 .

It is a cyclic number.

It is not a de Polignac number, because 21115421 - 2² = 21115417 is a prime.

It is a super-2 number, since 2×21115421² = 891722008014482, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21115421.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21115427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10557710 + 10557711.

It is an arithmetic number, because the mean of its divisors is an integer number (10557711).

Almost surely, 2^21115421 is an apocalyptic number.

It is an amenable number.

21115421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21115421 is an equidigital number, since it uses as much as digits as its factorization.

21115421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 80, while the sum is 17.

The square root of 21115421 is about 4595.1519017330. The cubic root of 21115421 is about 276.3969512238.

Adding to 21115421 its reverse (12451112), we get a palindrome (33566533).

The spelling of 21115421 in words is "twenty-one million, one hundred fifteen thousand, four hundred twenty-one".