21099011209956 has 225 divisors, whose sum is σ = 58670697818271. Its totient is φ = 6611801261184.

The previous prime is 21099011209919. The next prime is 21099011209961. The reversal of 21099011209956 is 65990211099012.

The square root of 21099011209956 is 4593366.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 2 ways, for example, as 6548143216356 + 14550867993600 = 2558934^2 + 3814560^2 .

It is a super-2 number, since 2×21099011209956² (a number of 27 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 74 ways as a sum of consecutive naturals, for example, 23894689491 + ... + 23894690373.

Almost surely, 2^{21099011209956} is an apocalyptic number.

21099011209956 is the 4593366-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21099011209956

21099011209956 is an abundant number, since it is smaller than the sum of its proper divisors (37571686608315).

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

21099011209956 is an frugal number, since it uses more digits than its factorization.

21099011209956 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1850 (or 905 counting only the distinct ones).

The product of its (nonzero) digits is 787320, while the sum is 54.

The spelling of 21099011209956 in words is "twenty-one trillion, ninety-nine billion, eleven million, two hundred nine thousand, nine hundred fifty-six".