A094285 Right leading diagonal of the triangle described in comments.

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

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 A371239 A376561

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