19781987 has 2 divisors, whose sum is σ = 19781988. Its totient is φ = 19781986.

The previous prime is 19781981. The next prime is 19781989. The reversal of 19781987 is 78918791.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 19781987 - 2¹⁰ = 19780963 is a prime.

Together with 19781989, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (19781981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9890993 + 9890994.

It is an arithmetic number, because the mean of its divisors is an integer number (9890994).

Almost surely, 2^19781987 is an apocalyptic number.

19781987 is a deficient number, since it is larger than the sum of its proper divisors (1).

19781987 is an equidigital number, since it uses as much as digits as its factorization.

19781987 is an evil number, because the sum of its binary digits is even.

The product of its digits is 254016, while the sum is 50.

The square root of 19781987 is about 4447.6945713482. The cubic root of 19781987 is about 270.4518588242.

The spelling of 19781987 in words is "nineteen million, seven hundred eighty-one thousand, nine hundred eighty-seven".