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A207338 Triangle read by rows in which row n lists the prime factors of n with repetition, with a(1) = 1, but with the primes of the form 4k + 1 multiplied by -1. 2
1, 2, 3, 2, 2, -5, 2, 3, 7, 2, 2, 2, 3, 3, 2, -5, 11, 2, 2, 3, -13, 2, 7, 3, -5, 2, 2, 2, 2, -17, 2, 3, 3, 19, 2, 2, -5, 3, 7, 2, 11, 23, 2, 2, 2, 3, -5, -5, 2, -13, 3, 3, 3, 2, 2, 7, -29, 2, 3, -5, 31, 2, 2, 2, 2, 2, 3, 11, 2, -17, -5, 7, 2, 2, 3, 3, -37 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The row products of triangle give A209662. Also the row products of triangle divided by n give A209661. The mentioned sequences are related to an infinite series which is equal to pi, due to Leonhard Euler.

LINKS

Table of n, a(n) for n=1..77.

EXAMPLE

Written as a triangle begins:

1;

2;

3;

2, 2;

-5;

2, 3;

7;

2, 2, 2;

3, 3;

2, -5;

11;

2, 2, 3;

-13;

2, 7;

3, -5;

2, 2, 2, 2;

CROSSREFS

Absolute values give A027746.

Cf. A002144, A002145, A209661, A209662.

Sequence in context: A225176 A118665 A225243 * A027746 A240230 A238689

Adjacent sequences:  A207335 A207336 A207337 * A207339 A207340 A207341

KEYWORD

sign,tabf

AUTHOR

Omar E. Pol, Apr 15 2012

STATUS

approved

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Last modified December 12 16:38 EST 2017. Contains 295949 sequences.