19978997 has 2 divisors, whose sum is σ = 19978998. Its totient is φ = 19978996.

The previous prime is 19978991. The next prime is 19979017. The reversal of 19978997 is 79987991.

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., 14638276 + 5340721 = 3826^2 + 2311^2 .

It is a cyclic number.

It is not a de Polignac number, because 19978997 - 2¹² = 19974901 is a prime.

It is a super-2 number, since 2×19978997² = 798320642252018, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19978991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9989498 + 9989499.

It is an arithmetic number, because the mean of its divisors is an integer number (9989499).

Almost surely, 2^19978997 is an apocalyptic number.

It is an amenable number.

19978997 is a deficient number, since it is larger than the sum of its proper divisors (1).

19978997 is an equidigital number, since it uses as much as digits as its factorization.

19978997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2571912, while the sum is 59.

The square root of 19978997 is about 4469.7871313968. The cubic root of 19978997 is about 271.3467101903.

The spelling of 19978997 in words is "nineteen million, nine hundred seventy-eight thousand, nine hundred ninety-seven".