81601643 has 2 divisors, whose sum is σ = 81601644. Its totient is φ = 81601642.

The previous prime is 81601633. The next prime is 81601727. The reversal of 81601643 is 34610618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81601643 - 2⁴ = 81601627 is a prime.

It is not a weakly prime, because it can be changed into another prime (81601633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40800821 + 40800822.

It is an arithmetic number, because the mean of its divisors is an integer number (40800822).

Almost surely, 2^81601643 is an apocalyptic number.

81601643 is a deficient number, since it is larger than the sum of its proper divisors (1).

81601643 is an equidigital number, since it uses as much as digits as its factorization.

81601643 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 81601643 is about 9033.3627736298. The cubic root of 81601643 is about 433.7434881243.

Subtracting from 81601643 its reverse (34610618), we obtain a square (46991025 = 6855²).

The spelling of 81601643 in words is "eighty-one million, six hundred one thousand, six hundred forty-three".