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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

Table of n, a(n) for n=2..50.

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 A266001 A062879

Adjacent sequences:  A094282 A094283 A094284 * A094286 A094287 A094288

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 January 24 00:05 EST 2022. Contains 350515 sequences. (Running on oeis4.)