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A129297
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Nonnegative integers m such that m^2-1 has no divisors d with 1<d<m-1.
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3
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0, 1, 2, 3, 4, 6, 12, 18, 30, 42, 60, 72, 102, 108, 138, 150, 180, 192, 198, 228, 240, 270, 282, 312, 348, 420, 432, 462, 522, 570, 600, 618, 642, 660, 810, 822, 828, 858, 882, 1020, 1032, 1050, 1062, 1092, 1152, 1230, 1278, 1290, 1302, 1320, 1428, 1452, 1482, 1488
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OFFSET
| 1,3
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COMMENTS
| A129296(a(n)) = #{1, a(n)-1} = 2;
a(n) = A014574(n-4) for n>4.
Since m^2-1 = (m+1)(m-1), this sequence is just 0,1,2,3, and the average of twin prime pairs A014574.
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EXAMPLE
| {1,41,43,1763} is the set of divisors of 42^2-1, therefore 42 is a term, A129296(42) = #{1,41} = 2.
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PROG
| (PARI) isA129297(n) = (n <= 3) || divisors(n^2-1)[2] >= n-1
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CROSSREFS
| Cf. A129293, A129295.
Sequence in context: A037393 A048330 A118651 * A018343 A102462 A018369
Adjacent sequences: A129294 A129295 A129296 * A129298 A129299 A129300
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KEYWORD
| nonn
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 09 2007
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