81909851 has 2 divisors, whose sum is σ = 81909852. Its totient is φ = 81909850.

The previous prime is 81909847. The next prime is 81909853. The reversal of 81909851 is 15890918.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81909851 - 2² = 81909847 is a prime.

Together with 81909853, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 81909799 and 81909808.

It is not a weakly prime, because it can be changed into another prime (81909853) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40954925 + 40954926.

It is an arithmetic number, because the mean of its divisors is an integer number (40954926).

Almost surely, 2^81909851 is an apocalyptic number.

81909851 is a deficient number, since it is larger than the sum of its proper divisors (1).

81909851 is an equidigital number, since it uses as much as digits as its factorization.

81909851 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 41.

The square root of 81909851 is about 9050.4061234842. The cubic root of 81909851 is about 434.2888826121.

The spelling of 81909851 in words is "eighty-one million, nine hundred nine thousand, eight hundred fifty-one".