21666402 has 12 divisors (see below), whose sum is σ = 46943910. Its totient is φ = 7222128.

The previous prime is 21666397. The next prime is 21666443. The reversal of 21666402 is 20466612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 16232841 + 5433561 = 4029^2 + 2331^2 .

It is an unprimeable number.

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 5 ways as a sum of consecutive naturals, for example, 601827 + ... + 601862.

Almost surely, 2^21666402 is an apocalyptic number.

21666402 is an abundant number, since it is smaller than the sum of its proper divisors (25277508).

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

21666402 is a wasteful number, since it uses less digits than its factorization.

21666402 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1203697 (or 1203694 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 21666402 is about 4654.7182514090. The cubic root of 21666402 is about 278.7804184331.

The spelling of 21666402 in words is "twenty-one million, six hundred sixty-six thousand, four hundred two".