A091089 Numbers which form a prime by appending a 3-digit odd number and form no primes by appending any 1- or 2-digit odd number not beginning with 0.

16557, 16718, 26378, 35921, 46524, 46867, 50018, 55187, 58374, 58452, 60850, 63714, 68771, 71299, 78035, 78269, 81661, 84213, 89052, 90157, 95490, 97080, 102892, 105690, 108682, 115558, 115994, 116138, 116305, 121097, 128192, 131194

Offset: 1

Author

Chuck Seggelin, Dec 18 2003

Keywords

• base
• nonn

Comments

Many numbers become prime by appending a one-digit odd number. Some numbers (such as 20, 32, 51, etc.) require a 2-digit odd number (A032352 has these). In the first 100000 values of n there are only 22 that require a 3-digit odd number.

Examples

			a(1)=16557 because 16557 is first number which requires a 3-digit odd number be appended to it to form a prime. 165571, 165573, 165575, ..., 165579, 1655711, 1655713, ..., 1655799 are all nonprime numbers. 16557103 is the first prime formed by appending odd numbers to 16657.
a(2) = 16718 because 16718111 is the first prime formed by appending odd numbers to 16718.
		

Links

• Robert Price, Table of n, a(n) for n = 1..23419
• Index entries for primes involving decimal expansion of n

Crossrefs

Cf. A032352 (a(n) requires at least a 2-digit odd number), A068695 (minimum odd number that must be appended to n to form a prime).

Extensions

Definition edited by N. J. A. Sloane, Nov 08 2020