21521212513 has 4 divisors (see below), whose sum is σ = 21676041520. Its totient is φ = 21366383508.

The previous prime is 21521212507. The next prime is 21521212523. The reversal of 21521212513 is 31521212512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21521212513 - 2¹³ = 21521204321 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521212523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 77414295 + ... + 77414572.

It is an arithmetic number, because the mean of its divisors is an integer number (5419010380).

Almost surely, 2^21521212513 is an apocalyptic number.

It is an amenable number.

21521212513 is a deficient number, since it is larger than the sum of its proper divisors (154829007).

21521212513 is a wasteful number, since it uses less digits than its factorization.

21521212513 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154829006.

The product of its digits is 1200, while the sum is 25.

Subtracting 21521212513 from its reverse (31521212512), we obtain a palindrome (9999999999).

The spelling of 21521212513 in words is "twenty-one billion, five hundred twenty-one million, two hundred twelve thousand, five hundred thirteen".