21521661621025 has 6 divisors (see below), whose sum is σ = 26686860410102. Its totient is φ = 17217329296800.

The previous prime is 21521661621011. The next prime is 21521661621029. The reversal of 21521661621025 is 52012616612512.

It can be written as a sum of positive squares in 3 ways, for example, as 155810193984 + 21365851427041 = 394728^2 + 4622321^2 .

It is not a de Polignac number, because 21521661621025 - 2⁵ = 21521661620993 is a prime.

It is a super-3 number, since 3×21521661621025³ (a number of 41 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521661621029) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 430433232396 + ... + 430433232445.

Almost surely, 2^{21521661621025} is an apocalyptic number.

21521661621025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21521661621025 is a deficient number, since it is larger than the sum of its proper divisors (5165198789077).

21521661621025 is an equidigital number, since it uses as much as digits as its factorization.

21521661621025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 860866464851 (or 860866464846 counting only the distinct ones).

The product of its (nonzero) digits is 86400, while the sum is 40.

The spelling of 21521661621025 in words is "twenty-one trillion, five hundred twenty-one billion, six hundred sixty-one million, six hundred twenty-one thousand, twenty-five".