21681516 has 24 divisors (see below), whose sum is σ = 50835904. Its totient is φ = 7192080.

The previous prime is 21681487. The next prime is 21681529. The reversal of 21681516 is 61518612.

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 in 7 ways as a sum of consecutive naturals, for example, 1750 + ... + 6813.

Almost surely, 2^21681516 is an apocalyptic number.

It is an amenable number.

21681516 is an abundant number, since it is smaller than the sum of its proper divisors (29154388).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21681516 is a wasteful number, since it uses less digits than its factorization.

21681516 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8781 (or 8779 counting only the distinct ones).

The product of its digits is 2880, while the sum is 30.

The square root of 21681516 is about 4656.3414823228. The cubic root of 21681516 is about 278.8452270382.

The spelling of 21681516 in words is "twenty-one million, six hundred eighty-one thousand, five hundred sixteen".