A032622 Numbers k such that k concatenated with k+7 is a prime.

2, 6, 20, 26, 30, 36, 44, 60, 62, 66, 74, 80, 86, 1004, 1034, 1046, 1086, 1094, 1104, 1136, 1142, 1194, 1200, 1206, 1214, 1224, 1250, 1262, 1266, 1290, 1292, 1296, 1320, 1326, 1332, 1346, 1350, 1352, 1356, 1364, 1370, 1380, 1404, 1416, 1434, 1472, 1496

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032612.

Programs

Maple

filter:= n -> isprime(n * 10^(1+ilog10(n+7)) + n + 7):
select(filter, [seq(i,i=2..10000,2)]); # Robert Israel, May 13 2025