20011221961 has 2 divisors, whose sum is σ = 20011221962. Its totient is φ = 20011221960.

The previous prime is 20011221949. The next prime is 20011221983. The reversal of 20011221961 is 16912211002.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16762221961 + 3249000000 = 129469^2 + 57000^2 .

It is a cyclic number.

It is not a de Polignac number, because 20011221961 - 2²⁹ = 19474351049 is a prime.

It is not a weakly prime, because it can be changed into another prime (20011221361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10005610980 + 10005610981.

It is an arithmetic number, because the mean of its divisors is an integer number (10005610981).

Almost surely, 2^20011221961 is an apocalyptic number.

It is an amenable number.

20011221961 is a deficient number, since it is larger than the sum of its proper divisors (1).

20011221961 is an equidigital number, since it uses as much as digits as its factorization.

20011221961 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 25.

Adding to 20011221961 its reverse (16912211002), we get a palindrome (36923432963).

The spelling of 20011221961 in words is "twenty billion, eleven million, two hundred twenty-one thousand, nine hundred sixty-one".