81694721 has 2 divisors, whose sum is σ = 81694722. Its totient is φ = 81694720.

The previous prime is 81694709. The next prime is 81694733. The reversal of 81694721 is 12749618.

It is a balanced prime because it is at equal distance from previous prime (81694709) and next prime (81694733).

It can be written as a sum of positive squares in only one way, i.e., 79834225 + 1860496 = 8935^2 + 1364^2 .

It is a cyclic number.

It is not a de Polignac number, because 81694721 - 2¹⁰ = 81693697 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (81694751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40847360 + 40847361.

It is an arithmetic number, because the mean of its divisors is an integer number (40847361).

Almost surely, 2^81694721 is an apocalyptic number.

It is an amenable number.

81694721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81694721 is an equidigital number, since it uses as much as digits as its factorization.

81694721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 24192, while the sum is 38.

The square root of 81694721 is about 9038.5132073810. The cubic root of 81694721 is about 433.9083403449.

The spelling of 81694721 in words is "eighty-one million, six hundred ninety-four thousand, seven hundred twenty-one".