21020061251 has 4 divisors (see below), whose sum is σ = 24022927152. Its totient is φ = 18017195352.

The previous prime is 21020061239. The next prime is 21020061287. The reversal of 21020061251 is 15216002012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21020061251 - 2¹⁴ = 21020044867 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21020061151) 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 3 ways as a sum of consecutive naturals, for example, 1501432940 + ... + 1501432953.

It is an arithmetic number, because the mean of its divisors is an integer number (6005731788).

Almost surely, 2^21020061251 is an apocalyptic number.

21020061251 is a deficient number, since it is larger than the sum of its proper divisors (3002865901).

21020061251 is an equidigital number, since it uses as much as digits as its factorization.

21020061251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3002865900.

The product of its (nonzero) digits is 240, while the sum is 20.

Adding to 21020061251 its reverse (15216002012), we get a palindrome (36236063263).

The spelling of 21020061251 in words is "twenty-one billion, twenty million, sixty-one thousand, two hundred fifty-one".