21655771281 has 45 divisors (see below), whose sum is σ = 32911493131. Its totient is φ = 14190836688.

The previous prime is 21655771237. The next prime is 21655771301. The reversal of 21655771281 is 18217755612.

The square root of 21655771281 is 147159.

It is a perfect power (a square), and thus also a powerful number.

21655771281 is a `hidden beast` number, since 2 + 1 + 6 + 557 + 7 + 12 + 81 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21218292225 + 437479056 = 145665^2 + 20916^2 .

It is not a de Polignac number, because 21655771281 - 2⁹ = 21655770769 is a prime.

It is a super-2 number, since 2×21655771281² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21655771211) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 109927675 + ... + 109927871.

Almost surely, 2^21655771281 is an apocalyptic number.

21655771281 is the 147159-th square number.

21655771281 is the 73580-th centered octagonal number.

It is an amenable number.

21655771281 is a deficient number, since it is larger than the sum of its proper divisors (11255721850).

21655771281 is an frugal number, since it uses more digits than its factorization.

21655771281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 572 (or 283 counting only the distinct ones).

The product of its digits is 235200, while the sum is 45.

The spelling of 21655771281 in words is "twenty-one billion, six hundred fifty-five million, seven hundred seventy-one thousand, two hundred eighty-one".