

A094285


Right leading diagonal of the triangle described in comments.


0



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

2,1


COMMENTS

Below is the triangle in which the left half of the nth 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.


LINKS



EXAMPLE

In the row for n = 5 the terms corresponding to 4,3,2 are 9,11,13 respectively.


PROG

(PARI) findsps(last, ps) = {new = last+1; while(factor(new)[, 2] != ps, new++); new; }
a(n) = {last = n; orig = last  1; for (i = 1, n1, ps = factor(orig)[, 2]; last = findsps(last, ps); orig ; ); return (last); } \\ Michel Marcus, Feb 05 2014


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



