661265640 has 256 divisors, whose sum is σ = 2629324800. Its totient is φ = 144536832.

The previous prime is 661265621. The next prime is 661265641. The reversal of 661265640 is 46562166.

It is a happy number.

661265640 is a `hidden beast` number, since 6 + 6 + 1 + 2 + 6 + 5 + 640 = 666.

661265640 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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).

It is a junction number, because it is equal to n+sod(n) for n = 661265595 and 661265604.

It is not an unprimeable number, because it can be changed into a prime (661265641) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 171979 + ... + 175781.

It is an arithmetic number, because the mean of its divisors is an integer number (10270800).

Almost surely, 2^661265640 is an apocalyptic number.

661265640 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 661265640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1314662400).

661265640 is an abundant number, since it is smaller than the sum of its proper divisors (1968059160).

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

661265640 is a wasteful number, since it uses less digits than its factorization.

661265640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3853 (or 3843 counting only the distinct ones).

The product of its (nonzero) digits is 51840, while the sum is 36.

The square root of 661265640 is about 25715.0858446944. The cubic root of 661265640 is about 871.2149493902.

The spelling of 661265640 in words is "six hundred sixty-one million, two hundred sixty-five thousand, six hundred forty".