81733721 has 2 divisors, whose sum is σ = 81733722. Its totient is φ = 81733720.

The previous prime is 81733711. The next prime is 81733723. The reversal of 81733721 is 12733718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81360400 + 373321 = 9020^2 + 611^2 .

It is a cyclic number.

It is not a de Polignac number, because 81733721 - 2⁶ = 81733657 is a prime.

It is a super-2 number, since 2×81733721² = 13360802297011682, which contains 22 as substring.

Together with 81733723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81733723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40866860 + 40866861.

It is an arithmetic number, because the mean of its divisors is an integer number (40866861).

Almost surely, 2^81733721 is an apocalyptic number.

It is an amenable number.

81733721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81733721 is an equidigital number, since it uses as much as digits as its factorization.

81733721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7056, while the sum is 32.

The square root of 81733721 is about 9040.6703844350. The cubic root of 81733721 is about 433.9773767646.

The spelling of 81733721 in words is "eighty-one million, seven hundred thirty-three thousand, seven hundred twenty-one".