21215421 has 12 divisors (see below), whose sum is σ = 30764448. Its totient is φ = 14088264.

The previous prime is 21215401. The next prime is 21215437. The reversal of 21215421 is 12451212.

21215421 is a `hidden beast` number, since 2 + 121 + 542 + 1 = 666.

It is not a de Polignac number, because 21215421 - 2⁹ = 21214909 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21215394 and 21215403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215401) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2115 + ... + 6848.

It is an arithmetic number, because the mean of its divisors is an integer number (2563704).

Almost surely, 2^21215421 is an apocalyptic number.

It is an amenable number.

21215421 is a deficient number, since it is larger than the sum of its proper divisors (9549027).

21215421 is a wasteful number, since it uses less digits than its factorization.

21215421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9232 (or 9229 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21215421 is about 4606.0200824573. The cubic root of 21215421 is about 276.8325913948.

Adding to 21215421 its reverse (12451212), we get a palindrome (33666633).

The spelling of 21215421 in words is "twenty-one million, two hundred fifteen thousand, four hundred twenty-one".