21601666 has 8 divisors (see below), whose sum is σ = 32424444. Its totient is φ = 10793520.

The previous prime is 21601639. The next prime is 21601667. The reversal of 21601666 is 66610612.

It can be written as a sum of positive squares in 2 ways, for example, as 21206025 + 395641 = 4605^2 + 629^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21601667) 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 3 ways as a sum of consecutive naturals, for example, 1476 + ... + 6736.

Almost surely, 2^21601666 is an apocalyptic number.

21601666 is a deficient number, since it is larger than the sum of its proper divisors (10822778).

21601666 is a wasteful number, since it uses less digits than its factorization.

21601666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7316.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21601666 is about 4647.7592450556. The cubic root of 21601666 is about 278.5024899132.

The spelling of 21601666 in words is "twenty-one million, six hundred one thousand, six hundred sixty-six".