A181450 Numbers k such that 11 is the largest prime factor of k^2 - 1.

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

Offset: 1

Author

Artur Jasinski, Oct 21 2010

Keywords

• fini
• full
• nonn

Comments

Numbers k such that A076605(k) = 11.

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.

Crossrefs

Row 5 of A223701.

Cf. A076605, A175607, A181447-A181449, A181451-A181470, A181568.

Programs

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

Mathematica

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

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