19906781 has 2 divisors, whose sum is σ = 19906782. Its totient is φ = 19906780.

The previous prime is 19906763. The next prime is 19906793. The reversal of 19906781 is 18760991.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11115556 + 8791225 = 3334^2 + 2965^2 .

It is an emirp because it is prime and its reverse (18760991) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19906781 is a prime.

It is a super-3 number, since 3×19906781³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19906751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9953390 + 9953391.

It is an arithmetic number, because the mean of its divisors is an integer number (9953391).

Almost surely, 2^19906781 is an apocalyptic number.

It is an amenable number.

19906781 is a deficient number, since it is larger than the sum of its proper divisors (1).

19906781 is an equidigital number, since it uses as much as digits as its factorization.

19906781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 27216, while the sum is 41.

The square root of 19906781 is about 4461.7015812356. The cubic root of 19906781 is about 271.0193792508.

The spelling of 19906781 in words is "nineteen million, nine hundred six thousand, seven hundred eighty-one".