81919251 has 6 divisors (see below), whose sum is σ = 118327820. Its totient is φ = 54612828.

The previous prime is 81919247. The next prime is 81919259. The reversal of 81919251 is 15291918.

It is not a de Polignac number, because 81919251 - 2² = 81919247 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81919259) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4551061 + ... + 4551078.

Almost surely, 2^81919251 is an apocalyptic number.

81919251 is a deficient number, since it is larger than the sum of its proper divisors (36408569).

81919251 is a wasteful number, since it uses less digits than its factorization.

81919251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9102145 (or 9102142 counting only the distinct ones).

The product of its digits is 6480, while the sum is 36.

The square root of 81919251 is about 9050.9254222980. The cubic root of 81919251 is about 434.3054950191.

The spelling of 81919251 in words is "eighty-one million, nine hundred nineteen thousand, two hundred fifty-one".