21256740521 has 4 divisors (see below), whose sum is σ = 21257202000. Its totient is φ = 21256279044.

The previous prime is 21256740503. The next prime is 21256740539. The reversal of 21256740521 is 12504765212.

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 an interprime number because it is at equal distance from previous prime (21256740503) and next prime (21256740539).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21256740521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21250740521) 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, 152891 + ... + 256688.

It is an arithmetic number, because the mean of its divisors is an integer number (5314300500).

Almost surely, 2^21256740521 is an apocalyptic number.

It is an amenable number.

21256740521 is a deficient number, since it is larger than the sum of its proper divisors (461479).

21256740521 is an equidigital number, since it uses as much as digits as its factorization.

21256740521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 461478.

The product of its (nonzero) digits is 33600, while the sum is 35.

The spelling of 21256740521 in words is "twenty-one billion, two hundred fifty-six million, seven hundred forty thousand, five hundred twenty-one".