Sequences

Numbers k such that k prefixed by '2' and followed by '3' is prime.

Numbers k such that k prefixed by '4' and followed by '3' is prime.

Numbers k such that k prefixed by '5' and followed by '3' is prime.

Numbers k such that k prefixed by '6' and followed by '3' is prime.

Numbers k such that k prefixed by '7' and followed by '3' is prime.

Numbers k such that k prefixed by '8' and followed by '3' is prime.

Numbers k such that k prefixed by '9' and followed by '3' is prime.

Numbers k such that k prefixed by '1' and followed by '7' is prime.

Numbers k such that k prefixed by '2' and followed by '7' is prime.

Integers that when prefixed by '3' and followed by '7' yield a prime.

Numbers k such that k prefixed by '4' and followed by '7' is prime.

Numbers k such that k prefixed by '5' and followed by '7' is prime.

Numbers k such that k prefixed by '6' and followed by '7' is a prime.

Numbers k such that k prefixed by '8' and followed by '7' is prime.

Numbers k such that k prefixed by '9' and followed by '7' is prime.

Numbers k such that k prefixed by '1' and followed by '9' is a prime.

Numbers k such that k prefixed by '2' and followed by '9' is prime.

Numbers k such that k prefixed by '3' and followed by '9' is prime.

Numbers k such that k prefixed by '4' and followed by '9' is prime.

Numbers k such that k prefixed by '5' and followed by '9' is prime.

Numbers k such that k prefixed by '6' and followed by '9' is a prime.

Numbers k such that k prefixed by '7' and followed by '9' is prime.

Numbers k such that k prefixed by '8' and followed by '9' is prime.

All 81 combinations of prefixing and following a(n) by a single digit are nonprime.

Palindromes that cannot be prefixed and followed by any digit to form a prime.

a(n) cannot be prefixed or followed by any digit to form a prime ('empty' prefixes allowed).

Composite numbers k such that all the decimal concatenations ik and ikj (i, j = 1...9) are also composite.

a(n) cannot be prefixed or followed by any digit to form a prime ('empty' prefixes and suffixes are allowed).

a(n) = floor( (Pi/e)^n ).

Numbers k such that k is a substring of 2^k.

a(0) = 0; for n > 0, a(n) = number of proper divisors of n (divisors of n which are less than n).

a(1) = 1; for n > 1, a(n) = largest proper divisor of n (that is, for n>1, maximum divisor d of n in range 1 <= d < n).

Super-2 Numbers (2 * n^2 contains substring '22' in its decimal expansion).

Super-4 Numbers (4 * n^4 contains substring '4444' in its decimal expansion).

Super-5 Numbers (5 * n^5 contains substring '55555' in its decimal expansion).

Super-6 Numbers (6 * n^6 contains substring '666666' in its decimal expansion).

Super-7 Numbers (7 * n^7 contains substring '7777777' in its decimal expansion).

Super-8 Numbers (8 * n^8 contains substring '88888888' in its decimal expansion).

Super-9 Numbers (9*n^9 contains substring '999999999' in its decimal expansion).

Palindromic Super-2 Numbers.

Palindromic Super-3 Numbers.

Palindromic Super-4 Numbers.

Palindromic Super-5 Numbers.

Palindromic Super-6 Numbers.

Palindromic Super-7 Numbers.

Palindromic Super-8 Numbers.

Palindromic Super-9 Numbers.

Undulating primes (digits alternate).

Take list of primes, move left digit of each term to end of previous term.

Take list of squares, move left digit of each term to end of previous term.