A181450 - OEIS

A181450

Numbers n such that 11 is the largest prime factor of n^2 - 1.

10, 21, 23, 34, 43, 65, 76, 89, 109, 111, 197, 199, 241, 351, 485, 769, 881, 1079, 6049, 19601

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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(5) = 19601; primepi(11) = 5.

LINKS

MATHEMATICA

Select[Range[20000], FactorInteger[#^2-1][[-1, 1]]==11&]

PROG

(Magma) [ n: n in [2..20000] | m eq 11 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // Klaus Brockhaus, Feb 18 2011

(PARI) is(n)=n=n^2-1; forprime(p=2, 7, n/=p^valuation(n, p)); n>1 && 11^valuation(n, 11)==n \\ Charles R Greathouse IV, Jul 01 2013

CROSSREFS

KEYWORD

fini,full,nonn

AUTHOR

STATUS

approved