21651490 has 32 divisors (see below), whose sum is σ = 45494784. Its totient is φ = 7264320.

The previous prime is 21651473. The next prime is 21651491. The reversal of 21651490 is 9415612.

21651490 is a nontrivial binomial coefficient, being equal to C(6581, 2).

It is not an unprimeable number, because it can be changed into a prime (21651491) 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, 1 + ... + 6580.

It is an arithmetic number, because the mean of its divisors is an integer number (1421712).

Almost surely, 2^21651490 is an apocalyptic number.

21651490 is the 6580-th triangular number.

21651490 is the 2194-th centered nonagonal number.

21651490 is an abundant number, since it is smaller than the sum of its proper divisors (23843294).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21651490 is a wasteful number, since it uses less digits than its factorization.

21651490 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6642.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21651490 is about 4653.1161601662. The cubic root of 21651490 is about 278.7164464563.

It can be divided in two parts, 2165 and 1490, that added together give a triangular number (3655 = T₈₅).

The spelling of 21651490 in words is "twenty-one million, six hundred fifty-one thousand, four hundred ninety".