21505256165376 has 585 divisors, whose sum is σ = 65703038647521. Its totient is φ = 7009041383424.

The previous prime is 21505256165357. The next prime is 21505256165531. The reversal of 21505256165376 is 67356165250512.

The square root of 21505256165376 is 4637376.

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

21505256165376 is a `hidden beast` number, since 2 + 1 + 5 + 0 + 5 + 2 + 561 + 6 + 5 + 3 + 76 = 666.

It can be written as a sum of positive squares in only one way, i.e., 9656680550400 + 11848575614976 = 3107520^2 + 3442176^2 .

It is a super-2 number, since 2×21505256165376² (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 (17) of ones.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 221703671760 + ... + 221703671856.

Almost surely, 2^{21505256165376} is an apocalyptic number.

21505256165376 is the 4637376-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21505256165376

21505256165376 is an abundant number, since it is smaller than the sum of its proper divisors (44197782482145).

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

21505256165376 is an frugal number, since it uses more digits than its factorization.

21505256165376 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 396 (or 185 counting only the distinct ones).

The product of its (nonzero) digits is 11340000, while the sum is 54.

The spelling of 21505256165376 in words is "twenty-one trillion, five hundred five billion, two hundred fifty-six million, one hundred sixty-five thousand, three hundred seventy-six".