661445172 has 54 divisors (see below), whose sum is σ = 1697728578. Its totient is φ = 217137888.

The previous prime is 661445149. The next prime is 661445173. The reversal of 661445172 is 271544166.

It can be written as a sum of positive squares in only one way, i.e., 543635856 + 117809316 = 23316^2 + 10854^2 .

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 (661445173) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 159558 + ... + 163650.

Almost surely, 2^661445172 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 661445172, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (848864289).

661445172 is an abundant number, since it is smaller than the sum of its proper divisors (1036283406).

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

661445172 is a wasteful number, since it uses less digits than its factorization.

661445172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4237 (or 4165 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 661445172 is about 25718.5763991711. The cubic root of 661445172 is about 871.2937864969.

The spelling of 661445172 in words is "six hundred sixty-one million, four hundred forty-five thousand, one hundred seventy-two".