661021205 has 16 divisors (see below), whose sum is σ = 865950960. Its totient is φ = 481448448.

The previous prime is 661021199. The next prime is 661021211. The reversal of 661021205 is 502120166.

It is an interprime number because it is at equal distance from previous prime (661021199) and next prime (661021211).

It can be written as a sum of positive squares in 8 ways, for example, as 1661521 + 659359684 = 1289^2 + 25678^2 .

It is not a de Polignac number, because 661021205 - 2⁴ = 661021189 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 64910 + ... + 74399.

It is an arithmetic number, because the mean of its divisors is an integer number (54121935).

Almost surely, 2^661021205 is an apocalyptic number.

661021205 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

661021205 is a deficient number, since it is larger than the sum of its proper divisors (204929755).

661021205 is a wasteful number, since it uses less digits than its factorization.

661021205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 139400.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 661021205 is about 25710.3326505123. The cubic root of 661021205 is about 871.1075887683.

The spelling of 661021205 in words is "six hundred sixty-one million, twenty-one thousand, two hundred five".