19921621 has 2 divisors, whose sum is σ = 19921622. Its totient is φ = 19921620.

The previous prime is 19921607. The next prime is 19921631. The reversal of 19921621 is 12612991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18610596 + 1311025 = 4314^2 + 1145^2 .

It is a cyclic number.

It is not a de Polignac number, because 19921621 - 2⁵ = 19921589 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19921631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9960810 + 9960811.

It is an arithmetic number, because the mean of its divisors is an integer number (9960811).

Almost surely, 2^19921621 is an apocalyptic number.

It is an amenable number.

19921621 is a deficient number, since it is larger than the sum of its proper divisors (1).

19921621 is an equidigital number, since it uses as much as digits as its factorization.

19921621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 31.

The square root of 19921621 is about 4463.3643140573. The cubic root of 19921621 is about 271.0867085457.

The spelling of 19921621 in words is "nineteen million, nine hundred twenty-one thousand, six hundred twenty-one".