16

This number is a composite.

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16 is probably the only positive integer N such that if the positive integers are listed in rows of N, then the first row with no prime is immediately followed by another row with no prime. If N=16, then the first row with no prime is 1329, 1330, 1331, 1332, 1333, 1334, 1335, 1336, 1337, 1338, 1339, 1340, 1341, 1342, 1343, 1344. The next row is 1345, 1346, 1347, 1348, 1349, 1350, 1351, 1352, 1353, 1354, 1355, 1356, 1357, 1358, 1359, 1360, which contains no prime. [Jacobs]