21665208068100 has 81 divisors (see below), whose sum is σ = 67908828756223. Its totient is φ = 5777351581440.

The previous prime is 21665208068089. The next prime is 21665208068129. The reversal of 21665208068100 is 186080256612.

The square root of 21665208068100 is 4654590.

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

21665208068100 is a `hidden beast` number, since 2 + 1 + 66 + 520 + 8 + 0 + 68 + 1 + 0 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 634765945284 + 21030442122816 = 796722^2 + 4585896^2 .

It is a super-2 number, since 2×21665208068100² (a number of 27 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 139560124 + ... + 139715276.

Almost surely, 2^{21665208068100} is an apocalyptic number.

21665208068100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21665208068100 is the 4654590-th square number.

It is an amenable number.

21665208068100 is an abundant number, since it is smaller than the sum of its proper divisors (46243620688123).

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

21665208068100 is an frugal number, since it uses more digits than its factorization.

21665208068100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 310326 (or 155163 counting only the distinct ones).

The product of its (nonzero) digits is 276480, while the sum is 45.

The spelling of 21665208068100 in words is "twenty-one trillion, six hundred sixty-five billion, two hundred eight million, sixty-eight thousand, one hundred".