81130921 has 2 divisors, whose sum is σ = 81130922. Its totient is φ = 81130920.

The previous prime is 81130877. The next prime is 81130939. The reversal of 81130921 is 12903118.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 60528400 + 20602521 = 7780^2 + 4539^2 .

It is a cyclic number.

It is not a de Polignac number, because 81130921 - 2¹⁵ = 81098153 is a prime.

It is not a weakly prime, because it can be changed into another prime (81130991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40565460 + 40565461.

It is an arithmetic number, because the mean of its divisors is an integer number (40565461).

Almost surely, 2^81130921 is an apocalyptic number.

It is an amenable number.

81130921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81130921 is an equidigital number, since it uses as much as digits as its factorization.

81130921 is an evil number, because the sum of its binary digits is even.

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

The square root of 81130921 is about 9007.2704522513. The cubic root of 81130921 is about 432.9078576556.

The spelling of 81130921 in words is "eighty-one million, one hundred thirty thousand, nine hundred twenty-one".