21809402 has 8 divisors (see below), whose sum is σ = 34638516. Its totient is φ = 10263232.

The previous prime is 21809401. The next prime is 21809413. The reversal of 21809402 is 20490812.

It can be written as a sum of positive squares in 2 ways, for example, as 19616041 + 2193361 = 4429^2 + 1481^2 .

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

It is a plaindrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (21809401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 320693 + ... + 320760.

Almost surely, 2^21809402 is an apocalyptic number.

21809402 is a deficient number, since it is larger than the sum of its proper divisors (12829114).

21809402 is a wasteful number, since it uses less digits than its factorization.

21809402 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 641472.

The product of its (nonzero) digits is 1152, while the sum is 26.

The square root of 21809402 is about 4670.0537470141. The cubic root of 21809402 is about 279.3923984413.

The spelling of 21809402 in words is "twenty-one million, eight hundred nine thousand, four hundred two".