21651316 has 6 divisors (see below), whose sum is σ = 37889810. Its totient is φ = 10825656.

The previous prime is 21651307. The next prime is 21651323. The reversal of 21651316 is 61315612.

It can be written as a sum of positive squares in only one way, i.e., 21344400 + 306916 = 4620^2 + 554^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2706411 + ... + 2706418.

Almost surely, 2^21651316 is an apocalyptic number.

It is an amenable number.

21651316 is a deficient number, since it is larger than the sum of its proper divisors (16238494).

21651316 is a wasteful number, since it uses less digits than its factorization.

21651316 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5412833 (or 5412831 counting only the distinct ones).

The product of its digits is 1080, while the sum is 25.

The square root of 21651316 is about 4653.0974629810. The cubic root of 21651316 is about 278.7156998288.

Adding to 21651316 its reverse (61315612), we get a palindrome (82966928).

It can be divided in two parts, 2165 and 1316, that added together give a square (3481 = 59²).

The spelling of 21651316 in words is "twenty-one million, six hundred fifty-one thousand, three hundred sixteen".