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21242721 = 37080907
BaseRepresentation
bin101000100001…
…0001101100001
31110222020112110
41101002031201
520414231341
62035145533
7345363063
oct121021541
943866473
1021242721
1110a99a75
1271452a9
134529c76
142b6d733
151ce9216
hex1442361

21242721 has 4 divisors (see below), whose sum is σ = 28323632. Its totient is φ = 14161812.

The previous prime is 21242717. The next prime is 21242729. The reversal of 21242721 is 12724212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21242721 - 22 = 21242717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21242729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3540451 + ... + 3540456.

It is an arithmetic number, because the mean of its divisors is an integer number (7080908).

Almost surely, 221242721 is an apocalyptic number.

It is an amenable number.

21242721 is a deficient number, since it is larger than the sum of its proper divisors (7080911).

21242721 is an equidigital number, since it uses as much as digits as its factorization.

21242721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7080910.

The product of its digits is 448, while the sum is 21.

The square root of 21242721 is about 4608.9826426230. The cubic root of 21242721 is about 276.9512832084.

Adding to 21242721 its reverse (12724212), we get a palindrome (33966933).

The spelling of 21242721 in words is "twenty-one million, two hundred forty-two thousand, seven hundred twenty-one".

Divisors: 1 3 7080907 21242721