81561405 has 16 divisors (see below), whose sum is σ = 130642560. Its totient is φ = 43451328.

The previous prime is 81561397. The next prime is 81561409. The reversal of 81561405 is 50416518.

It is not a de Polignac number, because 81561405 - 2³ = 81561397 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81561409) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14184 + ... + 19086.

It is an arithmetic number, because the mean of its divisors is an integer number (8165160).

Almost surely, 2^81561405 is an apocalyptic number.

It is an amenable number.

81561405 is a deficient number, since it is larger than the sum of its proper divisors (49081155).

81561405 is a wasteful number, since it uses less digits than its factorization.

81561405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6020.

The product of its (nonzero) digits is 4800, while the sum is 30.

The square root of 81561405 is about 9031.1353106905. The cubic root of 81561405 is about 433.6721830242.

The spelling of 81561405 in words is "eighty-one million, five hundred sixty-one thousand, four hundred five".