21521155551 has 32 divisors (see below), whose sum is σ = 33197219328. Its totient is φ = 12147148800.

The previous prime is 21521155549. The next prime is 21521155571. The reversal of 21521155551 is 15555112512.

It is not a de Polignac number, because 21521155551 - 2¹ = 21521155549 is a prime.

It is a super-2 number, since 2×21521155551² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521155571) 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 31 ways as a sum of consecutive naturals, for example, 1055251 + ... + 1075451.

It is an arithmetic number, because the mean of its divisors is an integer number (1037413104).

Almost surely, 2^21521155551 is an apocalyptic number.

21521155551 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21521155551 is a deficient number, since it is larger than the sum of its proper divisors (11676063777).

21521155551 is a wasteful number, since it uses less digits than its factorization.

21521155551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20831.

The product of its digits is 12500, while the sum is 33.

The spelling of 21521155551 in words is "twenty-one billion, five hundred twenty-one million, one hundred fifty-five thousand, five hundred fifty-one".