Properties of the Number 991

Nine Hundred Ninety-One

Basics

Value: 990 → 991 → 992

Parity: odd

Prime: Yes

Previous Prime: 983

Next Prime: 997

Digit Sum: 19

Digital Root: 1

Palindrome: No

Factorization: 991

Divisors: 1, 991

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1111011111

Octal: 1737

Duodecimal: 6A7

Hexadecimal: 3df

Square: 982081

Square Root: 31.480152477394387

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: Yes

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Central polygonal numbers (the Lazy Caterer's sequence): n(n+1)/2 + 1; or, maximal number of pieces formed when slicing a pancake with n cuts. A124

Prime-indexed primes: primes with prime subscripts. A6450

Primes having only {1, 2, 9} as digits. A385776

Emirps (primes whose reversal is a different prime). A6567

a(n) = n + (n+1)². A28387

Primes of the form 10·n+1. A30430

Primes whose reversal in base 10 is also prime (called "palindromic primes" by David Wells, although that name usually refers to A002385). Also called reversible primes. A7500

Primes of the form 8n+7, that is, primes congruent to -1 mod 8. A7522

Primes p such that the decimal expansion of its base-9 conversion is also prime. A65727

Primes followed by a gap of 6, i.e., next prime is p + 6. A31924