12561661440 has 560 divisors, whose sum is σ = 46371460608. Its totient is φ = 3260694528.

The previous prime is 12561661433. The next prime is 12561661487. The reversal of 12561661440 is 4416616521.

12561661440 is a `hidden beast` number, since 1 + 2 + 56 + 166 + 1 + 440 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 12561661395 and 12561661404.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 98910657 + ... + 98910783.

Almost surely, 2^12561661440 is an apocalyptic number.

12561661440 is a gapful number since it is divisible by the number (10) 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 12561661440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23185730304).

12561661440 is an abundant number, since it is smaller than the sum of its proper divisors (33809799168).

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

12561661440 is an frugal number, since it uses more digits than its factorization.

12561661440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221 (or 190 counting only the distinct ones).

The product of its (nonzero) digits is 34560, while the sum is 36.

The spelling of 12561661440 in words is "twelve billion, five hundred sixty-one million, six hundred sixty-one thousand, four hundred forty".