21122061781 has 4 divisors (see below), whose sum is σ = 21274019200. Its totient is φ = 20970104364.

The previous prime is 21122061767. The next prime is 21122061833. The reversal of 21122061781 is 18716022112.

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 21122061781 - 2⁵ = 21122061749 is a prime.

It is a super-2 number, since 2×21122061781² (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 (21122061731) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 75978501 + ... + 75978778.

It is an arithmetic number, because the mean of its divisors is an integer number (5318504800).

Almost surely, 2^21122061781 is an apocalyptic number.

It is an amenable number.

21122061781 is a deficient number, since it is larger than the sum of its proper divisors (151957419).

21122061781 is a wasteful number, since it uses less digits than its factorization.

21122061781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 151957418.

The product of its (nonzero) digits is 2688, while the sum is 31.

Adding to 21122061781 its reverse (18716022112), we get a palindrome (39838083893).

The spelling of 21122061781 in words is "twenty-one billion, one hundred twenty-two million, sixty-one thousand, seven hundred eighty-one".