20181720 has 128 divisors (see below), whose sum is σ = 69128640. Its totient is φ = 4669440.

The previous prime is 20181671. The next prime is 20181731. The reversal of 20181720 is 2718102.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 26140 + ... + 26900.

Almost surely, 2^20181720 is an apocalyptic number.

20181720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20181720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34564320).

20181720 is an abundant number, since it is smaller than the sum of its proper divisors (48946920).

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

20181720 is a wasteful number, since it uses less digits than its factorization.

20181720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 805 (or 801 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 21.

The square root of 20181720 is about 4492.4069272496. The cubic root of 20181720 is about 272.2613908808.

Adding to 20181720 its reverse (2718102), we get a palindrome (22899822).

The spelling of 20181720 in words is "twenty million, one hundred eighty-one thousand, seven hundred twenty".