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21690991 = 73789941
BaseRepresentation
bin101001010111…
…1101001101111
31111211000110001
41102233221233
521023102431
62052525131
7352241020
oct122575157
944730401
1021690991
1111275843
1273207a7
13465600a
142c48c47
151d86e61
hex14afa6f

21690991 has 16 divisors (see below), whose sum is σ = 25773120. Its totient is φ = 17867520.

The previous prime is 21690983. The next prime is 21691003. The reversal of 21690991 is 19909612.

21690991 is a nontrivial binomial coefficient, being equal to C(6587, 2).

It is a cyclic number.

It is not a de Polignac number, because 21690991 - 23 = 21690983 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21690991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21690961) 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, 22581 + ... + 23521.

It is an arithmetic number, because the mean of its divisors is an integer number (1610820).

Almost surely, 221690991 is an apocalyptic number.

21690991 is the 6586-th triangular number.

21690991 is the 2196-th centered nonagonal number.

21690991 is a deficient number, since it is larger than the sum of its proper divisors (4082129).

21690991 is an equidigital number, since it uses as much as digits as its factorization.

21690991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1074.

The product of its (nonzero) digits is 8748, while the sum is 37.

The square root of 21690991 is about 4657.3588008656. The cubic root of 21690991 is about 278.8858403384.

The spelling of 21690991 in words is "twenty-one million, six hundred ninety thousand, nine hundred ninety-one".

Divisors: 1 7 37 89 259 623 941 3293 6587 23051 34817 83749 243719 586243 3098713 21690991