20405664 has 36 divisors (see below), whose sum is σ = 58029426. Its totient is φ = 6801792.

The previous prime is 20405663. The next prime is 20405683. The reversal of 20405664 is 46650402.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 13749264 + 6656400 = 3708^2 + 2580^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a super-2 number, since 2×20405664² = 832782246561792, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20405663) 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 5 ways as a sum of consecutive naturals, for example, 35139 + ... + 35714.

Almost surely, 2^20405664 is an apocalyptic number.

20405664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

20405664 is an abundant number, since it is smaller than the sum of its proper divisors (37623762).

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

20405664 is a wasteful number, since it uses less digits than its factorization.

20405664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70869 (or 70858 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 27.

The square root of 20405664 is about 4517.2628880772. The cubic root of 20405664 is about 273.2647273119.

The spelling of 20405664 in words is "twenty million, four hundred five thousand, six hundred sixty-four".