login
A181447
Numbers k such that 3 is the largest prime factor of k^2 - 1.
29
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(2) = 17; primepi(3) = 2.
MATHEMATICA
Select[Range[20], FactorInteger[#^2-1][[-1, 1]]==3&]
PROG
(Magma) [ n: n in [2..20] | m eq 3 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // Klaus Brockhaus, Feb 17 2011
(PARI) is(n)=n=n^2-1; my(o=valuation(n, 3)); o && n>>valuation(n/3^o, 2)==1 \\ Charles R Greathouse IV, Jul 01 2013
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Artur Jasinski, Oct 21 2010
STATUS
approved