This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 11 11:30 EST 2018. Contains 318049 sequences. (Running on oeis4.)