20051621 has 2 divisors, whose sum is σ = 20051622. Its totient is φ = 20051620.

The previous prime is 20051617. The next prime is 20051623. The reversal of 20051621 is 12615002.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15100996 + 4950625 = 3886^2 + 2225^2 .

It is a cyclic number.

It is not a de Polignac number, because 20051621 - 2² = 20051617 is a prime.

Together with 20051623, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20051621.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20051623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10025810 + 10025811.

It is an arithmetic number, because the mean of its divisors is an integer number (10025811).

Almost surely, 2^20051621 is an apocalyptic number.

It is an amenable number.

20051621 is a deficient number, since it is larger than the sum of its proper divisors (1).

20051621 is an equidigital number, since it uses as much as digits as its factorization.

20051621 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 20051621 is about 4477.9036389811. The cubic root of 20051621 is about 271.6750959450.

Adding to 20051621 its reverse (12615002), we get a palindrome (32666623).

The spelling of 20051621 in words is "twenty million, fifty-one thousand, six hundred twenty-one".