19978901681 has 2 divisors, whose sum is σ = 19978901682. Its totient is φ = 19978901680.

The previous prime is 19978901659. The next prime is 19978901699. The reversal of 19978901681 is 18610987991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14470887025 + 5508014656 = 120295^2 + 74216^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19978901681 is a prime.

It is a super-2 number, since 2×19978901681² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 19978901681.

It is not a weakly prime, because it can be changed into another prime (19978901081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9989450840 + 9989450841.

It is an arithmetic number, because the mean of its divisors is an integer number (9989450841).

Almost surely, 2^19978901681 is an apocalyptic number.

It is an amenable number.

19978901681 is a deficient number, since it is larger than the sum of its proper divisors (1).

19978901681 is an equidigital number, since it uses as much as digits as its factorization.

19978901681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1959552, while the sum is 59.

The spelling of 19978901681 in words is "nineteen billion, nine hundred seventy-eight million, nine hundred one thousand, six hundred eighty-one".