81808815251 has 4 divisors (see below), whose sum is σ = 83195405400. Its totient is φ = 80422225104.

The previous prime is 81808815247. The next prime is 81808815281. The reversal of 81808815251 is 15251880818.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 15251880818 = 2 ⋅7625940409.

It is a cyclic number.

It is not a de Polignac number, because 81808815251 - 2² = 81808815247 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81808815196 and 81808815205.

It is not an unprimeable number, because it can be changed into a prime (81808815281) 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, 693294986 + ... + 693295103.

It is an arithmetic number, because the mean of its divisors is an integer number (20798851350).

Almost surely, 2^81808815251 is an apocalyptic number.

81808815251 is a deficient number, since it is larger than the sum of its proper divisors (1386590149).

81808815251 is a wasteful number, since it uses less digits than its factorization.

81808815251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1386590148.

The product of its (nonzero) digits is 204800, while the sum is 47.

The spelling of 81808815251 in words is "eighty-one billion, eight hundred eight million, eight hundred fifteen thousand, two hundred fifty-one".