21002773781 has 4 divisors (see below), whose sum is σ = 22912116864. Its totient is φ = 19093430700.

The previous prime is 21002773763. The next prime is 21002773807. The reversal of 21002773781 is 18737720012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21002773781 - 2²² = 20998579477 is a prime.

It is a super-2 number, since 2×21002773781² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002773751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 954671525 + ... + 954671546.

It is an arithmetic number, because the mean of its divisors is an integer number (5728029216).

Almost surely, 2^21002773781 is an apocalyptic number.

It is an amenable number.

21002773781 is a deficient number, since it is larger than the sum of its proper divisors (1909343083).

21002773781 is a wasteful number, since it uses less digits than its factorization.

21002773781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1909343082.

The product of its (nonzero) digits is 32928, while the sum is 38.

The spelling of 21002773781 in words is "twenty-one billion, two million, seven hundred seventy-three thousand, seven hundred eighty-one".