661661280 has 288 divisors, whose sum is σ = 2645068608. Its totient is φ = 147456000.

The previous prime is 661661257. The next prime is 661661281. The reversal of 661661280 is 82166166.

It is a tau number, because it is divible by the number of its divisors (288).

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 (661661281) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 412480 + ... + 414080.

It is an arithmetic number, because the mean of its divisors is an integer number (9184266).

Almost surely, 2^661661280 is an apocalyptic number.

661661280 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 661661280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1322534304).

661661280 is an abundant number, since it is smaller than the sum of its proper divisors (1983407328).

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

661661280 is a wasteful number, since it uses less digits than its factorization.

661661280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1670 (or 1659 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 661661280 is about 25722.7774550106. Note that the first 3 decimals coincide. The cubic root of 661661280 is about 871.3886661446.

It can be divided in two parts, 6616 and 61280, that added together give a triangular number (67896 = T₃₆₈).

The spelling of 661661280 in words is "six hundred sixty-one million, six hundred sixty-one thousand, two hundred eighty".