81216761 has 2 divisors, whose sum is σ = 81216762. Its totient is φ = 81216760.

The previous prime is 81216757. The next prime is 81216763. The reversal of 81216761 is 16761218.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81090025 + 126736 = 9005^2 + 356^2 .

It is a cyclic number.

It is not a de Polignac number, because 81216761 - 2² = 81216757 is a prime.

It is a super-2 number, since 2×81216761² = 13192324534662242, which contains 22 as substring.

Together with 81216763, it forms a pair of twin primes.

It is a Chen 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 (81216763) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40608380 + 40608381.

It is an arithmetic number, because the mean of its divisors is an integer number (40608381).

Almost surely, 2^81216761 is an apocalyptic number.

It is an amenable number.

81216761 is a deficient number, since it is larger than the sum of its proper divisors (1).

81216761 is an equidigital number, since it uses as much as digits as its factorization.

81216761 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4032, while the sum is 32.

The square root of 81216761 is about 9012.0342320699. The cubic root of 81216761 is about 433.0604822112.

Adding to 81216761 its reverse (16761218), we get a palindrome (97977979).

The spelling of 81216761 in words is "eighty-one million, two hundred sixteen thousand, seven hundred sixty-one".