81475721 has 2 divisors, whose sum is σ = 81475722. Its totient is φ = 81475720.

The previous prime is 81475699. The next prime is 81475759. The reversal of 81475721 is 12757418.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78517321 + 2958400 = 8861^2 + 1720^2 .

It is a cyclic number.

It is not a de Polignac number, because 81475721 - 2¹⁰ = 81474697 is a prime.

It is a super-2 number, since 2×81475721² = 13276586224939682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81475921) 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, 40737860 + 40737861.

It is an arithmetic number, because the mean of its divisors is an integer number (40737861).

Almost surely, 2^81475721 is an apocalyptic number.

It is an amenable number.

81475721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81475721 is an equidigital number, since it uses as much as digits as its factorization.

81475721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15680, while the sum is 35.

The square root of 81475721 is about 9026.3902530303. The cubic root of 81475721 is about 433.5202656345.

The spelling of 81475721 in words is "eighty-one million, four hundred seventy-five thousand, seven hundred twenty-one".