20211661 has 2 divisors, whose sum is σ = 20211662. Its totient is φ = 20211660.

The previous prime is 20211643. The next prime is 20211671. The reversal of 20211661 is 16611202.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 15625 = 4494^2 + 125^2 .

It is a cyclic number.

It is not a de Polignac number, because 20211661 - 2⁷ = 20211533 is a prime.

It is a super-2 number, since 2×20211661² = 817022480757842, which contains 22 as substring.

It is a plaindrome in base 16.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20211671) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10105830 + 10105831.

It is an arithmetic number, because the mean of its divisors is an integer number (10105831).

Almost surely, 2^20211661 is an apocalyptic number.

It is an amenable number.

20211661 is a deficient number, since it is larger than the sum of its proper divisors (1).

20211661 is an equidigital number, since it uses as much as digits as its factorization.

20211661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 20211661 is about 4495.7380929053. The cubic root of 20211661 is about 272.3959639892.

Adding to 20211661 its reverse (16611202), we get a palindrome (36822863).

The spelling of 20211661 in words is "twenty million, two hundred eleven thousand, six hundred sixty-one".