20101661 has 2 divisors, whose sum is σ = 20101662. Its totient is φ = 20101660.

The previous prime is 20101637. The next prime is 20101663. The reversal of 20101661 is 16610102.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14784025 + 5317636 = 3845^2 + 2306^2 .

It is a cyclic number.

It is not a de Polignac number, because 20101661 - 2¹⁴ = 20085277 is a prime.

Together with 20101663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20101663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10050830 + 10050831.

It is an arithmetic number, because the mean of its divisors is an integer number (10050831).

Almost surely, 2^20101661 is an apocalyptic number.

It is an amenable number.

20101661 is a deficient number, since it is larger than the sum of its proper divisors (1).

20101661 is an equidigital number, since it uses as much as digits as its factorization.

20101661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 20101661 is about 4483.4875933808. The cubic root of 20101661 is about 271.9009019405.

Adding to 20101661 its reverse (16610102), we get a palindrome (36711763).

The spelling of 20101661 in words is "twenty million, one hundred one thousand, six hundred sixty-one".