81615505778 has 8 divisors (see below), whose sum is σ = 122705992668. Its totient is φ = 40713508224.

The previous prime is 81615505729. The next prime is 81615505837. The reversal of 81615505778 is 87750551618.

It can be written as a sum of positive squares in 2 ways, for example, as 54780806809 + 26834698969 = 234053^2 + 163813^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a super-2 number, since 2×81615505778² (a number of 23 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47121251 + ... + 47122982.

Almost surely, 2^81615505778 is an apocalyptic number.

81615505778 is a deficient number, since it is larger than the sum of its proper divisors (41090486890).

81615505778 is a wasteful number, since it uses less digits than its factorization.

81615505778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94244668.

The product of its (nonzero) digits is 2352000, while the sum is 53.

The spelling of 81615505778 in words is "eighty-one billion, six hundred fifteen million, five hundred five thousand, seven hundred seventy-eight".