19911961 has 2 divisors, whose sum is σ = 19911962. Its totient is φ = 19911960.

The previous prime is 19911959. The next prime is 19911971. The reversal of 19911961 is 16911991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19527561 + 384400 = 4419^2 + 620^2 .

It is a cyclic number.

It is not a de Polignac number, because 19911961 - 2¹ = 19911959 is a prime.

Together with 19911959, 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 19911961.

It is not a weakly prime, because it can be changed into another prime (19911971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9955980 + 9955981.

It is an arithmetic number, because the mean of its divisors is an integer number (9955981).

Almost surely, 2^19911961 is an apocalyptic number.

It is an amenable number.

19911961 is a deficient number, since it is larger than the sum of its proper divisors (1).

19911961 is an equidigital number, since it uses as much as digits as its factorization.

19911961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4374, while the sum is 37.

The square root of 19911961 is about 4462.2820394950. The cubic root of 19911961 is about 271.0428847861.

The spelling of 19911961 in words is "nineteen million, nine hundred eleven thousand, nine hundred sixty-one".