251891993 has 4 divisors (see below), whose sum is σ = 252653328. Its totient is φ = 251130660.

The previous prime is 251891989. The next prime is 251892001. The reversal of 251891993 is 399198152.

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 251891993 - 2² = 251891989 is a prime.

It is a super-2 number, since 2×251891993² = 126899152275024098, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (251891903) 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, 380171 + ... + 380832.

It is an arithmetic number, because the mean of its divisors is an integer number (63163332).

Almost surely, 2^251891993 is an apocalyptic number.

It is an amenable number.

251891993 is a deficient number, since it is larger than the sum of its proper divisors (761335).

251891993 is an equidigital number, since it uses as much as digits as its factorization.

251891993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 761334.

The product of its digits is 174960, while the sum is 47.

The square root of 251891993 is about 15871.1056010601. The cubic root of 251891993 is about 631.5457073133.

The spelling of 251891993 in words is "two hundred fifty-one million, eight hundred ninety-one thousand, nine hundred ninety-three".