Number of the day: 1521

Properties of the number 1521:

1521 = 3² × 13² is the 1280^th composite number and is not squarefree.
1521 has 2 distinct prime factors, 9 divisors, 10 antidivisors and 936 totatives.
1521 = 39² is a perfect power of an emirpimes.
1521 has a semiprime digit sum 9 in base 10.
1521 has a semiprime digit product 10 in base 10.
1521 has a triangular digit product 10 in base 10.
1521 has sum of divisors equal to 2379 which is a sphenic number.
1521 = 39² is a perfect square.
1521 = (38 × 39)/2 + (39 × 40)/2 is the sum of at least 2 consecutive triangular numbers in 1 way. In fact, it is the sum of 2 triangular numbers.
1521 = 761² - 760² = 255² - 252² = 89² - 80² = 65² - 52² = 39² - 0² is the difference of 2 nonnegative squares in 5 ways.
1521 is the difference of 2 positive pentagonal numbers in 1 way.
1521 = 15² + 36² is the sum of 2 positive squares in 1 way.
1521 is the sum of 3 positive squares.
1521² = 585² + 1404² = 1071² + 1080² is the sum of 2 positive squares in 2 ways.
1521² is the sum of 3 positive squares.
1521 is a proper divisor of 991³ - 1.
1521 = '15' + '21' is the concatenation of 2 semiprime numbers.
1521 = '15' + '21' is the concatenation of 2 triangular numbers.
1521 is palindromic in (at least) the following bases: 15, 22, 38, -23, -31, -40, -76, -80, and -95.
1521 in base 13 = 900 and consists of only the digits '0' and '9'.
1521 in base 15 = 6b6 and consists of only the digits '6' and 'b'.
1521 in base 19 = 441 and consists of only the digits '1' and '4'.
1521 in base 21 = 399 and consists of only the digits '3' and '9'.
1521 in base 22 = 333 and consists of only the digit '3'.
1521 in base 27 = 229 and consists of only the digits '2' and '9'.
1521 in base 37 = 144 and consists of only the digits '1' and '4'.
1521 in base 38 = 121 and consists of only the digits '1' and '2'.
1521 in base 39 = 100 and consists of only the digits '0' and '1'.

The number 1521 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A000290: The squares: a(n) = n^2.
A001597: Perfect powers: m^k where m > 0 and k >= 2.
A003238: Number of rooted trees with n vertices in which vertices at the same level have the same degree.
A007955: Product of divisors of n.
A016754: Odd squares: a(n) = (2n+1)^2. Also centered octagonal numbers.
A057660: a(n) = Sum_{k=1..n} n/gcd(n,k).
A080335: Diagonal in square spiral or maze arrangement of natural numbers.
A085986: Squares of the squarefree semiprimes (p^2*q^2).
A195160: Generalized 11-gonal (or hendecagonal) numbers: m*(9*m - 7)/2 with m = 0, 1, -1, 2, -2, 3, -3, ...
A299287: Coordination sequence for "tcd" 3D uniform tiling.