21615668 has 6 divisors (see below), whose sum is σ = 37827426. Its totient is φ = 10807832.

The previous prime is 21615667. The next prime is 21615677. The reversal of 21615668 is 86651612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 20994724 + 620944 = 4582^2 + 788^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21615667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2701955 + ... + 2701962.

It is an arithmetic number, because the mean of its divisors is an integer number (6304571).

Almost surely, 2^21615668 is an apocalyptic number.

It is an amenable number.

21615668 is a deficient number, since it is larger than the sum of its proper divisors (16211758).

21615668 is a wasteful number, since it uses less digits than its factorization.

21615668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5403921 (or 5403919 counting only the distinct ones).

The product of its digits is 17280, while the sum is 35.

The square root of 21615668 is about 4649.2653183057. The cubic root of 21615668 is about 278.5626511620.

The spelling of 21615668 in words is "twenty-one million, six hundred fifteen thousand, six hundred sixty-eight".