81421981 has 2 divisors, whose sum is σ = 81421982. Its totient is φ = 81421980.

The previous prime is 81421961. The next prime is 81421987. The reversal of 81421981 is 18912418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 40896025 + 40525956 = 6395^2 + 6366^2 .

It is a cyclic number.

It is not a de Polignac number, because 81421981 - 2⁷ = 81421853 is a prime.

It is a super-2 number, since 2×81421981² = 13259077979928722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81421987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40710990 + 40710991.

It is an arithmetic number, because the mean of its divisors is an integer number (40710991).

Almost surely, 2^81421981 is an apocalyptic number.

It is an amenable number.

81421981 is a deficient number, since it is larger than the sum of its proper divisors (1).

81421981 is an equidigital number, since it uses as much as digits as its factorization.

81421981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 34.

The square root of 81421981 is about 9023.4129352479. The cubic root of 81421981 is about 433.4249304726.

The spelling of 81421981 in words is "eighty-one million, four hundred twenty-one thousand, nine hundred eighty-one".