81561745 has 4 divisors (see below), whose sum is σ = 97874100. Its totient is φ = 65249392.

The previous prime is 81561731. The next prime is 81561761. The reversal of 81561745 is 54716518.

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 11068929 + 70492816 = 3327^2 + 8396^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561745 - 2¹⁹ = 81037457 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8156170 + ... + 8156179.

It is an arithmetic number, because the mean of its divisors is an integer number (24468525).

Almost surely, 2^81561745 is an apocalyptic number.

It is an amenable number.

81561745 is a deficient number, since it is larger than the sum of its proper divisors (16312355).

81561745 is a wasteful number, since it uses less digits than its factorization.

81561745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16312354.

The product of its digits is 33600, while the sum is 37.

The square root of 81561745 is about 9031.1541344393. The cubic root of 81561745 is about 433.6727856309.

The spelling of 81561745 in words is "eighty-one million, five hundred sixty-one thousand, seven hundred forty-five".