20686644 has 72 divisors (see below), whose sum is σ = 58988160. Its totient is φ = 6264720.

The previous prime is 20686621. The next prime is 20686661. The reversal of 20686644 is 44668602.

20686644 = 352² + 353² + ... + 472².

It is a happy number.

20686644 is a `hidden beast` number, since 2 + 0 + 6 + 8 + 6 + 644 = 666.

It is a super-3 number, since 3×20686644³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 20686599 and 20686608.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 12277 + ... + 13859.

It is an arithmetic number, because the mean of its divisors is an integer number (819280).

Almost surely, 2^20686644 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20686644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29494080).

20686644 is an abundant number, since it is smaller than the sum of its proper divisors (38301516).

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

20686644 is a wasteful number, since it uses less digits than its factorization.

20686644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1618 (or 1599 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 36.

The square root of 20686644 is about 4548.2572486613. The cubic root of 20686644 is about 274.5132723733.

The spelling of 20686644 in words is "twenty million, six hundred eighty-six thousand, six hundred forty-four".