21523666 has 16 divisors (see below), whose sum is σ = 34309656. Its totient is φ = 10091776.

The previous prime is 21523651. The next prime is 21523669. The reversal of 21523666 is 66632512.

It can be written as a sum of positive squares in 4 ways, for example, as 9765625 + 11758041 = 3125^2 + 3429^2 .

It is not an unprimeable number, because it can be changed into a prime (21523669) 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 in 7 ways as a sum of consecutive naturals, for example, 9780 + ... + 11776.

Almost surely, 2^21523666 is an apocalyptic number.

21523666 is a deficient number, since it is larger than the sum of its proper divisors (12785990).

21523666 is a wasteful number, since it uses less digits than its factorization.

21523666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333.

The product of its digits is 12960, while the sum is 31.

The square root of 21523666 is about 4639.3605162781. The cubic root of 21523666 is about 278.1668770171.

The spelling of 21523666 in words is "twenty-one million, five hundred twenty-three thousand, six hundred sixty-six".