661581144 has 240 divisors, whose sum is σ = 2162932200. Its totient is φ = 182552832.

The previous prime is 661581143. The next prime is 661581149. The reversal of 661581144 is 441185166.

661581144 is a `hidden beast` number, since 6 + 61 + 581 + 14 + 4 = 666.

It is a super-2 number, since 2×661581144² = 875379220192697472, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

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

Its product of digits (23040) is a multiple of the sum of its prime divisors (144).

It is a junction number, because it is equal to n+sod(n) for n = 661581099 and 661581108.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661581143) by changing a digit.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 7433452 + ... + 7433540.

Almost surely, 2^661581144 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661581144, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1081466100).

661581144 is an abundant number, since it is smaller than the sum of its proper divisors (1501351056).

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

661581144 is a wasteful number, since it uses less digits than its factorization.

661581144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 172 (or 144 counting only the distinct ones).

The product of its digits is 23040, while the sum is 36.

The square root of 661581144 is about 25721.2197222449. The cubic root of 661581144 is about 871.3534857971.

The spelling of 661581144 in words is "six hundred sixty-one million, five hundred eighty-one thousand, one hundred forty-four".