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21601 has 2 divisors, whose sum is σ = 21602. Its totient is φ = 21600.

The previous prime is 21599. The next prime is 21611. The reversal of 21601 is 10612.

It can be divided in two parts, 21 and 601, that multiplied together give a palindrome (12621).

21601 is nontrivially palindromic in base 12.

It is an a-pointer prime, because the next prime (21611) can be obtained adding 21601 to its sum of digits (10).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21025 + 576 = 145^2 + 24^2 .

It is a cyclic number.

It is not a de Polignac number, because 21601 - 21 = 21599 is a prime.

Together with 21599, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10800 + 10801.

It is an arithmetic number, because the mean of its divisors is an integer number (10801).

221601 is an apocalyptic number.

It is an amenable number.

21601 is a deficient number, since it is larger than the sum of its proper divisors (1).

21601 is an equidigital number, since it uses as much as digits as its factorization.

21601 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21601 is about 146.9727865967. The cubic root of 21601 is about 27.8499627718.

The spelling of 21601 in words is "twenty-one thousand, six hundred one".