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21700721 = 7173631
BaseRepresentation
bin101001011001…
…0000001110001
31111211111210102
41102302001301
521023410341
62053042145
7352311260
oct122620161
944744712
1021700721
1111282089
127326355
13465a583
142c4c5d7
151d89c9b
hex14b2071

21700721 has 16 divisors (see below), whose sum is σ = 26392320. Its totient is φ = 17478720.

The previous prime is 21700711. The next prime is 21700741. The reversal of 21700721 is 12700712.

It is not a de Polignac number, because 21700721 - 210 = 21699697 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21700693 and 21700702.

It is not an unprimeable number, because it can be changed into a prime (21700711) 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, 34076 + ... + 34706.

It is an arithmetic number, because the mean of its divisors is an integer number (1649520).

Almost surely, 221700721 is an apocalyptic number.

It is an amenable number.

21700721 is a deficient number, since it is larger than the sum of its proper divisors (4691599).

21700721 is an frugal number, since it uses more digits than its factorization.

With its successor (21700722) it forms an eRAP, since the sums of their prime factors are consecutive (689 and 690).

21700721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 689 (or 655 counting only the distinct ones).

The product of its (nonzero) digits is 196, while the sum is 20.

The square root of 21700721 is about 4658.4032672151. The cubic root of 21700721 is about 278.9275343545.

Subtracting from 21700721 its reverse (12700712), we obtain a palindrome (9000009).

The spelling of 21700721 in words is "twenty-one million, seven hundred thousand, seven hundred twenty-one".

Divisors: 1 7 17 119 289 631 2023 4417 4913 10727 34391 75089 182359 1276513 3100103 21700721