21621916 has 6 divisors (see below), whose sum is σ = 37838360. Its totient is φ = 10810956.

The previous prime is 21621881. The next prime is 21621923. The reversal of 21621916 is 61912612.

It is a super-2 number, since 2×21621916² = 935014503022112, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2702736 + ... + 2702743.

Almost surely, 2^21621916 is an apocalyptic number.

It is an amenable number.

21621916 is a deficient number, since it is larger than the sum of its proper divisors (16216444).

21621916 is a wasteful number, since it uses less digits than its factorization.

21621916 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5405483 (or 5405481 counting only the distinct ones).

The product of its digits is 1296, while the sum is 28.

The square root of 21621916 is about 4649.9372038771. The cubic root of 21621916 is about 278.5894880499.

The spelling of 21621916 in words is "twenty-one million, six hundred twenty-one thousand, nine hundred sixteen".