21012220551 has 32 divisors (see below), whose sum is σ = 32372213760. Its totient is φ = 11874766176.

The previous prime is 21012220531. The next prime is 21012220573. The reversal of 21012220551 is 15502221012.

It is not a de Polignac number, because 21012220551 - 2¹³ = 21012212359 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012220531) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1383340 + ... + 1398446.

It is an arithmetic number, because the mean of its divisors is an integer number (1011631680).

Almost surely, 2^21012220551 is an apocalyptic number.

21012220551 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21012220551 is a deficient number, since it is larger than the sum of its proper divisors (11359993209).

21012220551 is a wasteful number, since it uses less digits than its factorization.

21012220551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15843.

The product of its (nonzero) digits is 400, while the sum is 21.

Adding to 21012220551 its reverse (15502221012), we get a palindrome (36514441563).

The spelling of 21012220551 in words is "twenty-one billion, twelve million, two hundred twenty thousand, five hundred fifty-one".