21221561456421 has 16 divisors (see below), whose sum is σ = 28518346858944. Its totient is φ = 14036542700544.

The previous prime is 21221561456299. The next prime is 21221561456423. The reversal of 21221561456421 is 12465416512212.

It is not a de Polignac number, because 21221561456421 - 2¹⁰ = 21221561455397 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221561456423) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37324326 + ... + 37888631.

It is an arithmetic number, because the mean of its divisors is an integer number (1782396678684).

Almost surely, 2^{21221561456421} is an apocalyptic number.

It is an amenable number.

21221561456421 is a deficient number, since it is larger than the sum of its proper divisors (7296785402523).

21221561456421 is a wasteful number, since it uses less digits than its factorization.

21221561456421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75213700.

The product of its digits is 230400, while the sum is 42.

Adding to 21221561456421 its reverse (12465416512212), we get a palindrome (33686977968633).

The spelling of 21221561456421 in words is "twenty-one trillion, two hundred twenty-one billion, five hundred sixty-one million, four hundred fifty-six thousand, four hundred twenty-one".