19781966 has 4 divisors (see below), whose sum is σ = 29672952. Its totient is φ = 9890982.

The previous prime is 19781963. The next prime is 19781969. The reversal of 19781966 is 66918791.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66918791 = 103 ⋅649697.

It is an interprime number because it is at equal distance from previous prime (19781963) and next prime (19781969).

It is a self number, because there is not a number n which added to its sum of digits gives 19781966.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19781963) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4945490 + ... + 4945493.

It is an arithmetic number, because the mean of its divisors is an integer number (7418238).

Almost surely, 2^19781966 is an apocalyptic number.

19781966 is a deficient number, since it is larger than the sum of its proper divisors (9890986).

19781966 is an equidigital number, since it uses as much as digits as its factorization.

19781966 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9890985.

The product of its digits is 163296, while the sum is 47.

The square root of 19781966 is about 4447.6922105739. The cubic root of 19781966 is about 270.4517631228.

The spelling of 19781966 in words is "nineteen million, seven hundred eighty-one thousand, nine hundred sixty-six".