login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A223701 Irregular triangle of numbers k such that prime(n) is the largest prime factor of k^2 - 1. 7
3, 2, 5, 7, 17, 4, 9, 11, 19, 26, 31, 49, 161, 6, 8, 13, 15, 29, 41, 55, 71, 97, 99, 127, 244, 251, 449, 4801, 8749, 10, 21, 23, 34, 43, 65, 76, 89, 109, 111, 197, 199, 241, 351, 485, 769, 881, 1079, 6049, 19601, 12, 14, 25, 27, 51, 53, 64, 79, 129, 131, 155 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Note that the first number of each row forms the sequence 3, 2, 4, 6, 10, 12,..., which is A039915. The rows, except the first, are in A181447-A181470.

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

Irregular triangle:

{3},

{2, 5, 7, 17},

{4, 9, 11, 19, 26, 31, 49, 161},

{6, 8, 13, 15, 29, 41, 55, 71, 97, 99, 127, 244, 251, 449, 4801, 8749}

MATHEMATICA

t = Table[FactorInteger[n^2 - 1][[-1, 1]], {n, 2, 10^5}]; Table[1 + Flatten[Position[t, Prime[n]]], {n, 6}]

CROSSREFS

Cf. A175607 (largest number k such that the greatest prime factor of k^2-1 is prime(n)).

Cf. A181447-A181470.

Cf. A223702-A223707 (related sequences).

Sequence in context: A171018 A239260 A013655 * A220519 A094894 A089334

Adjacent sequences:  A223698 A223699 A223700 * A223702 A223703 A223704

KEYWORD

nonn,tabf

AUTHOR

T. D. Noe, Apr 03 2013

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 12 21:10 EDT 2020. Contains 336440 sequences. (Running on oeis4.)