21513421 has 4 divisors (see below), whose sum is σ = 21541212. Its totient is φ = 21485632.

The previous prime is 21513413. The next prime is 21513433. The reversal of 21513421 is 12431512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4818025 + 16695396 = 2195^2 + 4086^2 .

It is a cyclic number.

It is not a de Polignac number, because 21513421 - 2³ = 21513413 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21514421) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12700 + ... + 14293.

It is an arithmetic number, because the mean of its divisors is an integer number (5385303).

Almost surely, 2^21513421 is an apocalyptic number.

It is an amenable number.

21513421 is a deficient number, since it is larger than the sum of its proper divisors (27791).

21513421 is an equidigital number, since it uses as much as digits as its factorization.

21513421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27790.

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

The square root of 21513421 is about 4638.2562456164. The cubic root of 21513421 is about 278.1227353433.

Adding to 21513421 its reverse (12431512), we get a palindrome (33944933).

The spelling of 21513421 in words is "twenty-one million, five hundred thirteen thousand, four hundred twenty-one".