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A181449 Numbers n such that 7 is the largest prime factor of n^2 - 1. 2
6, 8, 13, 15, 29, 41, 55, 71, 97, 99, 127, 244, 251, 449, 4801, 8749 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence is finite and complete, for proof see A175607.

Search for terms can be restricted to the range from 2 to A175607(4) = 8749; primepi(7) = 4.

LINKS

Table of n, a(n) for n=1..16.

MATHEMATICA

Select[Range[9000], FactorInteger[#^2-1][[-1, 1]]==7&]

PROG

(MAGMA) [ n: n in [2..9000] | m eq 7 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // Klaus Brockhaus, Feb 17 2011

(PARI) is(n)=n=n^2-1; forprime(p=2, 5, n/=p^valuation(n, p)); n>1 && 7^valuation(n, 7)==n \\ Charles R Greathouse IV, Jul 01 2013

CROSSREFS

Cf. A175607, A181447, A181448, A181450-A181470, A181568.

Sequence in context: A285678 A027706 A047336 * A315874 A315875 A315876

Adjacent sequences:  A181446 A181447 A181448 * A181450 A181451 A181452

KEYWORD

fini,full,nonn

AUTHOR

Artur Jasinski, Oct 21 2010

STATUS

approved

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Last modified September 18 12:45 EDT 2019. Contains 327170 sequences. (Running on oeis4.)