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Triangle read by rows: T(1,1) = 1; for n>=2, write the first n^2 integers in an n X n array beginning with 1 in the upper left proceeding left to right and top to bottom; then T(n,k) is the last prime in the k-th row.

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`%I #7 Apr 11 2013 08:36:23
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`%S 1,2,3,3,5,7,3,7,11,13,5,7,13,19,23,5,11,17,23,29,31,7,13,19,23,31,41,
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`%T 47,7,13,23,31,37,47,53,61,7,17,23,31,43,53,61,71,79,7,19,29,37,47,59,
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`%U 67,79,89,97,11,19,31,43,53,61,73,83,97,109,113,11,23,31,47,59,71,83,89
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`%N Triangle read by rows: T(1,1) = 1; for n>=2, write the first n^2 integers in an n X n array beginning with 1 in the upper left proceeding left to right and top to bottom; then T(n,k) is the last prime in the k-th row.
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`%C There is a prime in each row.
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`%D Paulo Ribenboim, "The Little Book Of Big Primes," Springer-Verlag, NY 1991, page 185.
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`%e Triangle begins
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`%e 1;
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`%e 2, 3;
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`%e 3, 5, 7;
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`%e 3, 7, 11, 13;
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`%e 5, 7, 13, 19, 23;
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`%t PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; Table[ PrevPrim[i*n + 1], {n, 2, 12}, {i, 1, n}]
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`%Y Cf. A092556, A083415.
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`%K nonn,tabl
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`%O 1,2
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`%A _Robert G. Wilson v_, Feb 27 2004
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