21537666 has 12 divisors (see below), whose sum is σ = 46664982. Its totient is φ = 7179216.

The previous prime is 21537661. The next prime is 21537667. The reversal of 21537666 is 66673512.

It can be written as a sum of positive squares in only one way, i.e., 20061441 + 1476225 = 4479^2 + 1215^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21537666.

It is not an unprimeable number, because it can be changed into a prime (21537661) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 598251 + ... + 598286.

Almost surely, 2^21537666 is an apocalyptic number.

21537666 is an abundant number, since it is smaller than the sum of its proper divisors (25127316).

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

21537666 is a wasteful number, since it uses less digits than its factorization.

21537666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1196545 (or 1196542 counting only the distinct ones).

The product of its digits is 45360, while the sum is 36.

The square root of 21537666 is about 4640.8690996407. The cubic root of 21537666 is about 278.2271748652.

The spelling of 21537666 in words is "twenty-one million, five hundred thirty-seven thousand, six hundred sixty-six".