20511221 has 2 divisors, whose sum is σ = 20511222. Its totient is φ = 20511220.

The previous prime is 20511217. The next prime is 20511251. The reversal of 20511221 is 12211502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12888100 + 7623121 = 3590^2 + 2761^2 .

It is a cyclic number.

It is not a de Polignac number, because 20511221 - 2² = 20511217 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20511196 and 20511205.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20511251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10255610 + 10255611.

It is an arithmetic number, because the mean of its divisors is an integer number (10255611).

Almost surely, 2^20511221 is an apocalyptic number.

It is an amenable number.

20511221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20511221 is an equidigital number, since it uses as much as digits as its factorization.

20511221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 20511221 is about 4528.9315517018. The cubic root of 20511221 is about 273.7351099398.

Adding to 20511221 its reverse (12211502), we get a palindrome (32722723).

The spelling of 20511221 in words is "twenty million, five hundred eleven thousand, two hundred twenty-one".