81921031 has 2 divisors, whose sum is σ = 81921032. Its totient is φ = 81921030.

The previous prime is 81921023. The next prime is 81921041. The reversal of 81921031 is 13012918.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81921031 - 2³ = 81921023 is a prime.

It is a super-2 number, since 2×81921031² = 13422110640205922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81920987 and 81921005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81921001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40960515 + 40960516.

It is an arithmetic number, because the mean of its divisors is an integer number (40960516).

Almost surely, 2^81921031 is an apocalyptic number.

81921031 is a deficient number, since it is larger than the sum of its proper divisors (1).

81921031 is an equidigital number, since it uses as much as digits as its factorization.

81921031 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 81921031 is about 9051.0237542501. The cubic root of 81921031 is about 434.3086406297.

Adding to 81921031 its reverse (13012918), we get a palindrome (94933949).

The spelling of 81921031 in words is "eighty-one million, nine hundred twenty-one thousand, thirty-one".