21257781061 has 6 divisors (see below), whose sum is σ = 23365990886. Its totient is φ = 19325255400.

The previous prime is 21257781047. The next prime is 21257781067. The reversal of 21257781061 is 16018775212.

It can be written as a sum of positive squares in only one way, i.e., 21255890436 + 1890625 = 145794^2 + 1375^2 .

It is not a de Polignac number, because 21257781061 - 2⁵ = 21257781029 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21257781067) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 87841950 + ... + 87842191.

Almost surely, 2^21257781061 is an apocalyptic number.

It is an amenable number.

21257781061 is a deficient number, since it is larger than the sum of its proper divisors (2108209825).

21257781061 is a wasteful number, since it uses less digits than its factorization.

21257781061 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 175684163 (or 175684152 counting only the distinct ones).

The product of its (nonzero) digits is 47040, while the sum is 40.

The spelling of 21257781061 in words is "twenty-one billion, two hundred fifty-seven million, seven hundred eighty-one thousand, sixty-one".