61638686640 has 200 divisors, whose sum is σ = 214527372048. Its totient is φ = 16402659840.

The previous prime is 61638686623. The next prime is 61638686699. The reversal of 61638686640 is 4668683616.

It is a super-2 number, since 2×61638686640² (a number of 22 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 3171994 + ... + 3191366.

Almost surely, 2^61638686640 is an apocalyptic number.

61638686640 is a gapful number since it is divisible by the number (60) 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 61638686640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (107263686024).

61638686640 is an abundant number, since it is smaller than the sum of its proper divisors (152888685408).

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

61638686640 is a wasteful number, since it uses less digits than its factorization.

61638686640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19889 (or 19874 counting only the distinct ones).

The product of its (nonzero) digits is 5971968, while the sum is 54.

The spelling of 61638686640 in words is "sixty-one billion, six hundred thirty-eight million, six hundred eighty-six thousand, six hundred forty".