21005216121525 has 144 divisors (see below), whose sum is σ = 38769920929344. Its totient is φ = 10020233502720.

The previous prime is 21005216121521. The next prime is 21005216121529. The reversal of 21005216121525 is 52512161250012.

It is an interprime number because it is at equal distance from previous prime (21005216121521) and next prime (21005216121529).

It is not a de Polignac number, because 21005216121525 - 2² = 21005216121521 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005216121521) by changing a digit.

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 143 ways as a sum of consecutive naturals, for example, 34180369 + ... + 34789481.

Almost surely, 2^{21005216121525} is an apocalyptic number.

21005216121525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21005216121525 is a deficient number, since it is larger than the sum of its proper divisors (17764704807819).

21005216121525 is a wasteful number, since it uses less digits than its factorization.

21005216121525 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 609240 (or 609218 counting only the distinct ones).

The product of its (nonzero) digits is 12000, while the sum is 33.

Adding to 21005216121525 its reverse (52512161250012), we get a palindrome (73517377371537).

The spelling of 21005216121525 in words is "twenty-one trillion, five billion, two hundred sixteen million, one hundred twenty-one thousand, five hundred twenty-five".