81404621 has 2 divisors, whose sum is σ = 81404622. Its totient is φ = 81404620.

The previous prime is 81404593. The next prime is 81404623. The reversal of 81404621 is 12640418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 41538025 + 39866596 = 6445^2 + 6314^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81404621 is a prime.

Together with 81404623, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81404623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40702310 + 40702311.

It is an arithmetic number, because the mean of its divisors is an integer number (40702311).

Almost surely, 2^81404621 is an apocalyptic number.

It is an amenable number.

81404621 is a deficient number, since it is larger than the sum of its proper divisors (1).

81404621 is an equidigital number, since it uses as much as digits as its factorization.

81404621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 81404621 is about 9022.4509419558. The cubic root of 81404621 is about 433.3941247389.

The spelling of 81404621 in words is "eighty-one million, four hundred four thousand, six hundred twenty-one".