21251516841 has 9 divisors (see below), whose sum is σ = 30697267159. Its totient is φ = 14167386336.

The previous prime is 21251516833. The next prime is 21251516879. The reversal of 21251516841 is 14861515212.

The square root of 21251516841 is 145779.

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

21251516841 is a `hidden beast` number, since 2 + 12 + 51 + 516 + 84 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 12951578025 + 8299938816 = 113805^2 + 91104^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 21251516841 - 2³ = 21251516833 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21251516796 and 21251516805.

It is not an unprimeable number, because it can be changed into a prime (21251516801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 413041 + ... + 461633.

Almost surely, 2^21251516841 is an apocalyptic number.

21251516841 is the 145779-th square number.

21251516841 is the 72890-th centered octagonal number.

It is an amenable number.

21251516841 is a deficient number, since it is larger than the sum of its proper divisors (9445750318).

21251516841 is an frugal number, since it uses more digits than its factorization.

21251516841 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 97192 (or 48596 counting only the distinct ones).

The product of its digits is 19200, while the sum is 36.

Multiplying 21251516841 by its sum of digits (36), we get a square (765054606276 = 874674²).

The spelling of 21251516841 in words is "twenty-one billion, two hundred fifty-one million, five hundred sixteen thousand, eight hundred forty-one".