21821428 has 6 divisors (see below), whose sum is σ = 38187506. Its totient is φ = 10910712.

The previous prime is 21821419. The next prime is 21821441. The reversal of 21821428 is 82412812.

It can be written as a sum of positive squares in only one way, i.e., 14915044 + 6906384 = 3862^2 + 2628^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21821396 and 21821405.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2727675 + ... + 2727682.

Almost surely, 2^21821428 is an apocalyptic number.

It is an amenable number.

21821428 is a deficient number, since it is larger than the sum of its proper divisors (16366078).

21821428 is a wasteful number, since it uses less digits than its factorization.

21821428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5455361 (or 5455359 counting only the distinct ones).

The product of its digits is 2048, while the sum is 28.

The square root of 21821428 is about 4671.3411350489. The cubic root of 21821428 is about 279.4437425909.

The spelling of 21821428 in words is "twenty-one million, eight hundred twenty-one thousand, four hundred twenty-eight".