251581987 has 2 divisors, whose sum is σ = 251581988. Its totient is φ = 251581986.

The previous prime is 251581961. The next prime is 251581999. The reversal of 251581987 is 789185152.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 251581987 - 2⁷ = 251581859 is a prime.

It is not a weakly prime, because it can be changed into another prime (251581087) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125790993 + 125790994.

It is an arithmetic number, because the mean of its divisors is an integer number (125790994).

Almost surely, 2^251581987 is an apocalyptic number.

251581987 is a deficient number, since it is larger than the sum of its proper divisors (1).

251581987 is an equidigital number, since it uses as much as digits as its factorization.

251581987 is an evil number, because the sum of its binary digits is even.

The product of its digits is 201600, while the sum is 46.

The square root of 251581987 is about 15861.3362299650. The cubic root of 251581987 is about 631.2865177449.

The spelling of 251581987 in words is "two hundred fifty-one million, five hundred eighty-one thousand, nine hundred eighty-seven".