This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A171637 Triangle read by rows in which row n lists the distinct primes of the distinct decompositions of 2n into unordered sums of two primes. 2
 2, 3, 3, 5, 3, 5, 7, 5, 7, 3, 7, 11, 3, 5, 11, 13, 5, 7, 11, 13, 3, 7, 13, 17, 3, 5, 11, 17, 19, 5, 7, 11, 13, 17, 19, 3, 7, 13, 19, 23, 5, 11, 17, 23, 7, 11, 13, 17, 19, 23, 3, 13, 19, 29, 3, 5, 11, 17, 23, 29, 31, 5, 7, 13, 17, 19, 23, 29, 31, 7, 19, 31, 3, 11, 17, 23, 29, 37, 5, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Each entry of the n-th row is a prime p from the n-th row of A002260 such that 2n-p is also prime. If A002260 is read as the antidiagonals of a square array, this sequence can be read as an irregular square array (see example below). The n-th row has length A035026(n). This sequence is the nonzero subsequence of A154725. - Jason Kimberley, Jul 08 2012 LINKS T. D. Noe, Rows n = 2..250, flattened EXAMPLE a(2)=2 because for row 2: 2*2=2+2; a(3)=3 because for row 3: 2*3=3+3; a(4)=3 and a(5)=5 because for row 4: 2*4=3+5; a(6)=3, a(7)=5 and a(8)=7 because for row 5: 2*5=3+7=5+5. The table starts: 2; 3; 3,5; 3,5,7; 5,7; 3,7,11; 3,5,11,13; 5,7,11,13; 3,7,13,17; 3,5,11,17,19; 5,7,11,13,17,19; 3,7,13,19,23; 5,11,17,23; 7,11,13,17,19,23; 3,13,19,29; 3,5,11,17,23,29,31; As an irregular square array [Jason Kimberley, Jul 08 2012]: 3 . 3 . 3 . . . 3 . 3 . . . 3 . 3 . . . . . . . . . . . . . . . . 5 . 5 . 5 . . . 5 . 5 . . . 5 . . . . . . . . . . . . . . 7 . 7 . 7 . . . 7 . 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. 11. 11. . . 11 . . . . . . . . 13. 13. 13. . . . . . . . . . . . . . . . . 17. 17 . . 19 MATHEMATICA Table[ps = Prime[Range[PrimePi[2*n]]]; Select[ps, MemberQ[ps, 2*n - #] &], {n, 2, 50}] (* T. D. Noe, Jan 27 2012 *) CROSSREFS Related triangles: A154720, A154721, A154722, A154723, A154724, A154725, A154726, A154727, A184995. - Jason Kimberley, Sep 03 2011 Sequence in context: A119912 A076368 A071049 * A140187 A214127 A111607 Adjacent sequences:  A171634 A171635 A171636 * A171638 A171639 A171640 KEYWORD nonn,tabf AUTHOR Juri-Stepan Gerasimov, Dec 13 2009 EXTENSIONS Keyword:tabl replaced by tabf, arbitrarily defined a(1) removed and entries checked by R. J. Mathar, May 22 2010 Definition clarified by N. J. A. Sloane, May 23 2010 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .