21351515403121 has 4 divisors (see below), whose sum is σ = 22040273964544. Its totient is φ = 20662756841700.

The previous prime is 21351515403103. The next prime is 21351515403131. The reversal of 21351515403121 is 12130451515312.

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 21351515403121 - 2⁷ = 21351515402993 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21351515403131) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 344379280665 + ... + 344379280726.

It is an arithmetic number, because the mean of its divisors is an integer number (5510068491136).

Almost surely, 2^{21351515403121} is an apocalyptic number.

It is an amenable number.

21351515403121 is a deficient number, since it is larger than the sum of its proper divisors (688758561423).

21351515403121 is an equidigital number, since it uses as much as digits as its factorization.

21351515403121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 688758561422.

The product of its (nonzero) digits is 18000, while the sum is 34.

Adding to 21351515403121 its reverse (12130451515312), we get a palindrome (33481966918433).

The spelling of 21351515403121 in words is "twenty-one trillion, three hundred fifty-one billion, five hundred fifteen million, four hundred three thousand, one hundred twenty-one".