1205665021 has 4 divisors (see below), whose sum is σ = 1315270944. Its totient is φ = 1096059100.

The previous prime is 1205665001. The next prime is 1205665079.

1205665021 is nontrivially palindromic in base 10.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1205665021 - 2²⁹ = 668794109 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1205665001) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54802945 + ... + 54802966.

It is an arithmetic number, because the mean of its divisors is an integer number (328817736).

Almost surely, 2^1205665021 is an apocalyptic number.

1205665021 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1205665021 is a deficient number, since it is larger than the sum of its proper divisors (109605923).

1205665021 is a wasteful number, since it uses less digits than its factorization.

1205665021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109605922.

The product of its (nonzero) digits is 3600, while the sum is 28.

The square root of 1205665021 is about 34722.6874103950. The cubic root of 1205665021 is about 1064.3281621632.

It can be divided in two parts, 12056 and 65021, that added together give a palindrome (77077).

The spelling of 1205665021 in words is "one billion, two hundred five million, six hundred sixty-five thousand, twenty-one".