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A094285
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Right leading diagonal of the triangle described in comments.
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0
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2, 5, 7, 13, 13, 31, 31, 59, 59, 59, 59, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 179, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 1381, 24671
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OFFSET
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2,1
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COMMENTS
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Below is the triangle in which the left half of the n-th row contains numbers from 2 to n and the mirror image about the leading column contains numbers in increasing order with the same prime signature.
Initial triangle starts:
2;
2 3;
2 3 4;
2 3 4 5 9;
Final triangle starts:
2;
2 3 5;
2 3 4 5 7;
2 3 4 5 9 11 13;
2 3 4 5 6 7 9 11 13;
2 3 4 5 6 7 10 11 25 29 31;
...
All terms of the sequence are primes since they are numbers with same prime signature as the numbers of the first column, that are all equal to 2, a prime.
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LINKS
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EXAMPLE
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In the row for n = 5 the terms corresponding to 4,3,2 are 9,11,13 respectively.
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PROG
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(PARI) findsps(last, ps) = {new = last+1; while(factor(new)[, 2] != ps, new++); new; }
a(n) = {last = n; orig = last - 1; for (i = 1, n-1, ps = factor(orig)[, 2]; last = findsps(last, ps); orig --; ); return (last); } \\ Michel Marcus, Feb 05 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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