A225055 - OEIS

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A225055

Irregular triangle which lists the three positions of 2*n-1 in A060819 in row n.

1, 2, 4, 3, 6, 12, 5, 10, 20, 7, 14, 28, 9, 18, 36, 11, 22, 44, 13, 26, 52, 15, 30, 60, 17, 34, 68, 19, 38, 76, 21, 42, 84, 23, 46, 92, 25, 50, 100, 27, 54, 108, 29, 58, 116, 31, 62, 124, 33, 66, 132, 35, 70, 140, 37, 74, 148

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

There are no multiples of 8 in the triangle.

A047592 contains a sorted list of all elements of the triangle.

The triangle is a member of a family of triangles with parameter k that list the k positions of 2*n-1: 2*n-1 in A000027 (k=1), A043547 the k=2 positions in A026741, the triangle 1,2,4,8; 3,6,12,24;... with the k=4 positions in A106609, or the triangle 1,2,4,8,16; 3,6,12,24,48;... with the k=5 positions in A106617.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

FORMULA

T(n,1) = 2*n-1. T(n,2) = 4*n-2. T(n,3) = 8*n-4.

EXAMPLE

1, 2, 4; # 1 at A060819(1), A060819(2) and A060819(4)

3, 6, 12; # 3 at A060819(3), A060819(6) and A060819(12)

5, 10, 20;

7, 14, 28;

9, 18, 36;

11, 22, 44;

13, 26, 52;

15, 30, 60;

MATHEMATICA

numberOfTriplets = 19; A060819 = Table[n/GCD[n, 4], {n, 1, 8*numberOfTriplets}]; Table[Position[A060819, 2*n-1], {n, 1, numberOfTriplets}] // Flatten (* Jean-François Alcover, Apr 30 2013 *)

CROSSREFS

Cf. A147587. A042968.

Sequence in context: A134561 A258046 A334384 * A341194 A120947 A222600

Adjacent sequences: A225052 A225053 A225054 * A225056 A225057 A225058

KEYWORD

nonn,tabf,easy

AUTHOR

Paul Curtz, Apr 26 2013

STATUS

approved