21506131 has 2 divisors, whose sum is σ = 21506132. Its totient is φ = 21506130.

The previous prime is 21506101. The next prime is 21506143. The reversal of 21506131 is 13160512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21506131 - 2¹¹ = 21504083 is a prime.

It is a super-2 number, since 2×21506131² = 925027341178322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21506099 and 21506108.

It is not a weakly prime, because it can be changed into another prime (21506101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10753065 + 10753066.

It is an arithmetic number, because the mean of its divisors is an integer number (10753066).

Almost surely, 2^21506131 is an apocalyptic number.

21506131 is a deficient number, since it is larger than the sum of its proper divisors (1).

21506131 is an equidigital number, since it uses as much as digits as its factorization.

21506131 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 21506131 is about 4637.4703233552. The cubic root of 21506131 is about 278.0913170672.

Adding to 21506131 its reverse (13160512), we get a palindrome (34666643).

It can be divided in two parts, 2150 and 6131, that added together give a square (8281 = 91²).

The spelling of 21506131 in words is "twenty-one million, five hundred six thousand, one hundred thirty-one".