21640642 has 16 divisors (see below), whose sum is σ = 33394680. Its totient is φ = 10513152.

The previous prime is 21640637. The next prime is 21640651. The reversal of 21640642 is 24604612.

It can be written as a sum of positive squares in 4 ways, for example, as 16883881 + 4756761 = 4109^2 + 2181^2 .

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 7 ways as a sum of consecutive naturals, for example, 10618 + ... + 12490.

Almost surely, 2^21640642 is an apocalyptic number.

21640642 is a deficient number, since it is larger than the sum of its proper divisors (11754038).

21640642 is a wasteful number, since it uses less digits than its factorization.

21640642 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2037.

The product of its (nonzero) digits is 2304, while the sum is 25.

The square root of 21640642 is about 4651.9503436731. The cubic root of 21640642 is about 278.6698904439.

The spelling of 21640642 in words is "twenty-one million, six hundred forty thousand, six hundred forty-two".