20991600 has 360 divisors, whose sum is σ = 89949600. Its totient is φ = 4515840.

The previous prime is 20991577. The next prime is 20991601. The reversal of 20991600 is 619902.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (360).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991601) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1234792 + ... + 1234808.

It is an arithmetic number, because the mean of its divisors is an integer number (249860).

Almost surely, 2^20991600 is an apocalyptic number.

20991600 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 20991600, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44974800).

20991600 is an abundant number, since it is smaller than the sum of its proper divisors (68958000).

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

20991600 is a wasteful number, since it uses less digits than its factorization.

20991600 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62 (or 34 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 20991600 is about 4581.6590881470. The cubic root of 20991600 is about 275.8556270766.

It can be divided in two parts, 209 and 91600, that added together give a square (91809 = 303²).

The spelling of 20991600 in words is "twenty million, nine hundred ninety-one thousand, six hundred".