A223701 Irregular triangle of numbers k such that prime(n) is the largest prime factor of k^2 - 1.

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

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: A350192 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