81157421 has 2 divisors, whose sum is σ = 81157422. Its totient is φ = 81157420.

The previous prime is 81157403. The next prime is 81157429. The reversal of 81157421 is 12475118.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 64224196 + 16933225 = 8014^2 + 4115^2 .

It is a cyclic number.

It is not a de Polignac number, because 81157421 - 2⁶ = 81157357 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81157429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40578710 + 40578711.

It is an arithmetic number, because the mean of its divisors is an integer number (40578711).

Almost surely, 2^81157421 is an apocalyptic number.

It is an amenable number.

81157421 is a deficient number, since it is larger than the sum of its proper divisors (1).

81157421 is an equidigital number, since it uses as much as digits as its factorization.

81157421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2240, while the sum is 29.

The square root of 81157421 is about 9008.7413660289. The cubic root of 81157421 is about 432.9549864579.

The spelling of 81157421 in words is "eighty-one million, one hundred fifty-seven thousand, four hundred twenty-one".