A181449 Numbers n such that 7 is the largest prime factor of n^2 - 1.

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

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