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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 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,1
COMMENTS
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.
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, n-1, ps = factor(orig)[, 2]; last = findsps(last, ps); orig --; ); return (last); } \\ Michel Marcus, Feb 05 2014
CROSSREFS
Cf. A093496.
Sequence in context: A092792 A238336 A083271 * A121218 A371239 A266001
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Apr 27 2004
EXTENSIONS
Edited and extended by Michel Marcus, Feb 05 2014
STATUS
approved

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Last modified June 21 05:50 EDT 2024. Contains 373540 sequences. (Running on oeis4.)