20019661 has 2 divisors, whose sum is σ = 20019662. Its totient is φ = 20019660.

The previous prime is 20019647. The next prime is 20019677. The reversal of 20019661 is 16691002.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11055625 + 8964036 = 3325^2 + 2994^2 .

It is a cyclic number.

It is not a de Polignac number, because 20019661 - 2¹⁵ = 19986893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20019631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10009830 + 10009831.

It is an arithmetic number, because the mean of its divisors is an integer number (10009831).

Almost surely, 2^20019661 is an apocalyptic number.

It is an amenable number.

20019661 is a deficient number, since it is larger than the sum of its proper divisors (1).

20019661 is an equidigital number, since it uses as much as digits as its factorization.

20019661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 20019661 is about 4474.3335816633. Note that the first 3 decimals coincide. The cubic root of 20019661 is about 271.5306794702.

The spelling of 20019661 in words is "twenty million, nineteen thousand, six hundred sixty-one".