81561404471 has 24 divisors (see below), whose sum is σ = 84793406544. Its totient is φ = 78445635840.

The previous prime is 81561404461. The next prime is 81561404473. The reversal of 81561404471 is 17440416518.

It is a de Polignac number, because none of the positive numbers 2^k-81561404471 is a prime.

It is a super-3 number, since 3×81561404471³ (a number of 34 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81561404473) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 56132381 + ... + 56133833.

It is an arithmetic number, because the mean of its divisors is an integer number (3533058606).

Almost surely, 2^81561404471 is an apocalyptic number.

81561404471 is a deficient number, since it is larger than the sum of its proper divisors (3232002073).

81561404471 is a wasteful number, since it uses less digits than its factorization.

81561404471 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1971 (or 1934 counting only the distinct ones).

The product of its (nonzero) digits is 107520, while the sum is 41.

The spelling of 81561404471 in words is "eighty-one billion, five hundred sixty-one million, four hundred four thousand, four hundred seventy-one".