81561061 has 4 divisors (see below), whose sum is σ = 83765452. Its totient is φ = 79356672.

The previous prime is 81561049. The next prime is 81561089. The reversal of 81561061 is 16016518.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 58232161 + 23328900 = 7631^2 + 4830^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561061 - 2¹⁷ = 81429989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81561761) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1102140 + ... + 1102213.

It is an arithmetic number, because the mean of its divisors is an integer number (20941363).

Almost surely, 2^81561061 is an apocalyptic number.

It is an amenable number.

81561061 is a deficient number, since it is larger than the sum of its proper divisors (2204391).

81561061 is a wasteful number, since it uses less digits than its factorization.

81561061 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2204390.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 81561061 is about 9031.1162654458. The cubic root of 81561061 is about 433.6715733264.

Adding to 81561061 its reverse (16016518), we get a palindrome (97577579).

The spelling of 81561061 in words is "eighty-one million, five hundred sixty-one thousand, sixty-one".