Properties of the Number 1891

One Thousand Eight Hundred Ninety-One

Basics

Value: 1890 → 1891 → 1892

Parity: odd

Prime: No

Previous Prime: 1889

Next Prime: 1901

Digit Sum: 19

Digital Root: 1

Palindrome: No

Factorization: 31 × 61

Divisors: 1, 31, 61, 1891

Polygonal

Triangular: Yes

Square: No

Pentagonal: No

Hexagonal: Yes

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 11101100011

Octal: 3543

Duodecimal: 1117

Hexadecimal: 763

Square: 3575881

Square Root: 43.485629810317796

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Hexagonal numbers: a(n) = n*(2·n-1). A384

a(n) = n + (n+1)². A28387

Centered triangular numbers: a(n) = 3·n*(n-1)/2 + 1. A5448

Centered pentagonal numbers: (5n²+5n+2)/2; crystal ball sequence for 3.3.3.4.4. planar net. A5891

Centered 9-gonal (also known as nonagonal or enneagonal) numbers. Every third triangular number, starting with a(1)=1. A60544

Numbers k for which 10k+1, 10k+3, 10k+7 and 10k+9 are primes. A7811

Triangular numbers (A000217) with prime indices. A34953

Pseudoprimes to base 3. A5935

Moebius transform of A064987, n*σ(n). A69097

a(n) = n² - n - 1. A165900