21001554251 has 4 divisors (see below), whose sum is σ = 21010097400. Its totient is φ = 20993011104.

The previous prime is 21001554247. The next prime is 21001554359. The reversal of 21001554251 is 15245510012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21001554251 - 2² = 21001554247 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21001554251.

It is not an unprimeable number, because it can be changed into a prime (21001554241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4267886 + ... + 4272803.

It is an arithmetic number, because the mean of its divisors is an integer number (5252524350).

Almost surely, 2^21001554251 is an apocalyptic number.

21001554251 is a deficient number, since it is larger than the sum of its proper divisors (8543149).

21001554251 is an equidigital number, since it uses as much as digits as its factorization.

21001554251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8543148.

The product of its (nonzero) digits is 2000, while the sum is 26.

The spelling of 21001554251 in words is "twenty-one billion, one million, five hundred fifty-four thousand, two hundred fifty-one".