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A180640 Primes P such that P < (largest prime factor of (P-1)) * (largest prime factor of (P+1)). 1
2, 3, 5, 11, 13, 23, 29, 37, 43, 47, 59, 61, 67, 73, 83, 103, 107, 113, 131, 137, 139, 149, 157, 167, 173, 179, 193, 211, 223, 227, 229, 233, 263, 269, 277, 281, 283, 293, 311, 313, 317, 331, 347, 353, 359, 367, 373, 383, 389, 397, 409, 421, 439, 443, 457, 467 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

Example: For n = 3, a(3)=11.

The prime P = 11

P-1 = 10 (largest prime factor of 10 is 5)

P+1 = 12 (largest prime factor of 12 is 3)

11 < 5*3.

MATHEMATICA

Select[Prime[Range[100]], #<(FactorInteger[#-1][[-1, 1]] FactorInteger[#+1][[-1, 1]])&]  (* From Harvey P. Dale, Feb 22 2011 *)

CROSSREFS

Cf. A180641. See also A103666, A103667.

Sequence in context: A287164 A020607 A235631 * A128425 A175565 A262831

Adjacent sequences:  A180637 A180638 A180639 * A180641 A180642 A180643

KEYWORD

nonn

AUTHOR

Karl Hovekamp, Sep 14 2010

EXTENSIONS

Initial term, i.e., 2, added by Harvey P. Dale, Feb 22 2011

STATUS

approved

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Last modified December 7 03:00 EST 2019. Contains 329836 sequences. (Running on oeis4.)