61511921856 has 672 divisors, whose sum is σ = 231305160960. Its totient is φ = 15850598400.

The previous prime is 61511921839. The next prime is 61511921869. The reversal of 61511921856 is 65812911516.

61511921856 is a `hidden beast` number, since 61 + 511 + 9 + 21 + 8 + 56 = 666.

It is a tau number, because it is divible by the number of its divisors (672).

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 196523556 + ... + 196523868.

Almost surely, 2^61511921856 is an apocalyptic number.

61511921856 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 61511921856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (115652580480).

61511921856 is an abundant number, since it is smaller than the sum of its proper divisors (169793239104).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

61511921856 is a wasteful number, since it uses less digits than its factorization.

61511921856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570 (or 547 counting only the distinct ones).

The product of its digits is 129600, while the sum is 45.

The spelling of 61511921856 in words is "sixty-one billion, five hundred eleven million, nine hundred twenty-one thousand, eight hundred fifty-six".