81265421 has 2 divisors, whose sum is σ = 81265422. Its totient is φ = 81265420.

The previous prime is 81265409. The next prime is 81265427. The reversal of 81265421 is 12456218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81252196 + 13225 = 9014^2 + 115^2 .

It is a cyclic number.

It is not a de Polignac number, because 81265421 - 2¹⁰ = 81264397 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81265427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40632710 + 40632711.

It is an arithmetic number, because the mean of its divisors is an integer number (40632711).

Almost surely, 2^81265421 is an apocalyptic number.

It is an amenable number.

81265421 is a deficient number, since it is larger than the sum of its proper divisors (1).

81265421 is an equidigital number, since it uses as much as digits as its factorization.

81265421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3840, while the sum is 29.

The square root of 81265421 is about 9014.7335512482. The cubic root of 81265421 is about 433.1469525232.

The spelling of 81265421 in words is "eighty-one million, two hundred sixty-five thousand, four hundred twenty-one".