81443561 has 2 divisors, whose sum is σ = 81443562. Its totient is φ = 81443560.

The previous prime is 81443497. The next prime is 81443567. The reversal of 81443561 is 16534418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66667225 + 14776336 = 8165^2 + 3844^2 .

It is a cyclic number.

It is not a de Polignac number, because 81443561 - 2⁶ = 81443497 is a prime.

It is not a weakly prime, because it can be changed into another prime (81443567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40721780 + 40721781.

It is an arithmetic number, because the mean of its divisors is an integer number (40721781).

Almost surely, 2^81443561 is an apocalyptic number.

It is an amenable number.

81443561 is a deficient number, since it is larger than the sum of its proper divisors (1).

81443561 is an equidigital number, since it uses as much as digits as its factorization.

81443561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 32.

The square root of 81443561 is about 9024.6086341736. The cubic root of 81443561 is about 433.4632185929.

Adding to 81443561 its reverse (16534418), we get a palindrome (97977979).

The spelling of 81443561 in words is "eighty-one million, four hundred forty-three thousand, five hundred sixty-one".