661012020 has 144 divisors (see below), whose sum is σ = 2132636688. Its totient is φ = 165150720.

The previous prime is 661011991. The next prime is 661012031. The reversal of 661012020 is 20210166.

It is a happy number.

661012020 is a `hidden beast` number, since 661 + 0 + 1 + 2 + 0 + 2 + 0 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 23853456 + 637158564 = 4884^2 + 25242^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 661011984 and 661012002.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1030900 + ... + 1031540.

It is an arithmetic number, because the mean of its divisors is an integer number (14809977).

Almost surely, 2^661012020 is an apocalyptic number.

661012020 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 661012020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1066318344).

661012020 is an abundant number, since it is smaller than the sum of its proper divisors (1471624668).

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

661012020 is a wasteful number, since it uses less digits than its factorization.

661012020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1010 (or 1005 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 661012020 is about 25710.1540252096. The cubic root of 661012020 is about 871.1035540212.

Adding to 661012020 its reverse (20210166), we get a palindrome (681222186).

It can be divided in two parts, 66101 and 2020, that added together give a square (68121 = 261²).

The spelling of 661012020 in words is "six hundred sixty-one million, twelve thousand, twenty".