21531668 has 6 divisors (see below), whose sum is σ = 37680426. Its totient is φ = 10765832.

The previous prime is 21531667. The next prime is 21531689. The reversal of 21531668 is 86613512.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 18079504 + 3452164 = 4252^2 + 1858^2 .

It is a super-2 number, since 2×21531668² = 927225453724448, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2691455 + ... + 2691462.

It is an arithmetic number, because the mean of its divisors is an integer number (6280071).

Almost surely, 2^21531668 is an apocalyptic number.

It is an amenable number.

21531668 is a deficient number, since it is larger than the sum of its proper divisors (16148758).

21531668 is a wasteful number, since it uses less digits than its factorization.

21531668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5382921 (or 5382919 counting only the distinct ones).

The product of its digits is 8640, while the sum is 32.

The square root of 21531668 is about 4640.2228394766. Note that the first 3 decimals coincide. The cubic root of 21531668 is about 278.2013447446.

The spelling of 21531668 in words is "twenty-one million, five hundred thirty-one thousand, six hundred sixty-eight".