21361661 has 8 divisors (see below), whose sum is σ = 22164600. Its totient is φ = 20563200.

The previous prime is 21361619. The next prime is 21361709. The reversal of 21361661 is 16616312.

It can be written as a sum of positive squares in 4 ways, for example, as 3880900 + 17480761 = 1970^2 + 4181^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21361661 - 2¹⁴ = 21345277 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21361661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21361261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10961 + ... + 12761.

It is an arithmetic number, because the mean of its divisors is an integer number (2770575).

Almost surely, 2^21361661 is an apocalyptic number.

It is an amenable number.

21361661 is a deficient number, since it is larger than the sum of its proper divisors (802939).

21361661 is a wasteful number, since it uses less digits than its factorization.

21361661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2239.

The product of its digits is 1296, while the sum is 26.

The square root of 21361661 is about 4621.8676960727. The cubic root of 21361661 is about 277.4672136142.

Adding to 21361661 its reverse (16616312), we get a palindrome (37977973).

It can be divided in two parts, 21361 and 661, that added together give a palindrome (22022).

The spelling of 21361661 in words is "twenty-one million, three hundred sixty-one thousand, six hundred sixty-one".