661515660 has 240 divisors, whose sum is σ = 2264213952. Its totient is φ = 160704000.

The previous prime is 661515649. The next prime is 661515661. The reversal of 661515660 is 66515166.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661515661) by changing a digit.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 2126905 + ... + 2127215.

Almost surely, 2^661515660 is an apocalyptic number.

661515660 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 661515660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1132106976).

661515660 is an abundant number, since it is smaller than the sum of its proper divisors (1602698292).

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

661515660 is a wasteful number, since it uses less digits than its factorization.

661515660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 446 (or 435 counting only the distinct ones).

The product of its (nonzero) digits is 32400, while the sum is 36.

The square root of 661515660 is about 25719.9467340039. The cubic root of 661515660 is about 871.3247356859.

The spelling of 661515660 in words is "six hundred sixty-one million, five hundred fifteen thousand, six hundred sixty".