21783206781 has 24 divisors (see below), whose sum is σ = 37523041920. Its totient is φ = 11906348256.

The previous prime is 21783206771. The next prime is 21783206833. The reversal of 21783206781 is 18760238712.

It is not a de Polignac number, because 21783206781 - 2¹⁸ = 21782944637 is a prime.

It is a super-2 number, since 2×21783206781² (a number of 21 digits) contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21783206761) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7515186 + ... + 7518083.

It is an arithmetic number, because the mean of its divisors is an integer number (1563460080).

Almost surely, 2^21783206781 is an apocalyptic number.

21783206781 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21783206781 is a deficient number, since it is larger than the sum of its proper divisors (15739835139).

21783206781 is a wasteful number, since it uses less digits than its factorization.

21783206781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15033305 (or 15033302 counting only the distinct ones).

The product of its (nonzero) digits is 225792, while the sum is 45.

The spelling of 21783206781 in words is "twenty-one billion, seven hundred eighty-three million, two hundred six thousand, seven hundred eighty-one".