This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A253016 #22 Jun 22 2025 21:31:47 %S A253016 71,142,284,355,497,710,994,1420,1491,1988,2485,2840,2982,3976,4970, %T A253016 5680,5964,7455,9940,11928,14910,19880,23856,29820,39760,59640,79520, %U A253016 119280,238560,477120 %N A253016 Numbers k such that 11^phi(k) == 1 (mod k^2), where phi(k) = A000010(k). %C A253016 No further terms up to 10^9. %C A253016 No more terms less than 10^10. - _Robert G. Wilson v_, Jan 18 2015 %C A253016 The first 30 terms are divisible by 71. Are there any terms not divisible by 71? - _Robert Israel_, Dec 30 2014 %C A253016 By Corollary 5.9 in Agoh, Dilcher, Skula (1997), if there are no further Wieferich primes to base 11 apart from 71, then the answer is no. - _Felix Fröhlich_, Dec 30 2014 %H A253016 T. Agoh, K. Dilcher and L. Skula, <a href="http://dx.doi.org/10.1006/jnth.1997.2162">Fermat Quotients for Composite Moduli</a>, J. Num. Theory, Vol. 66, Issue 1 (1997), 29-50. %p A253016 select(t -> 11 &^ numtheory:-phi(t) mod t^2 = 1, [$1..10^6]); # _Robert Israel_, Dec 30 2014 %t A253016 a253016[n_] := Select[Range[n], PowerMod[11,EulerPhi[#], #^2] == 1 &]; a253016[500000] (* _Michael De Vlieger_, Dec 29 2014; modified by _Robert G. Wilson v_, Jan 18 2015 *) %o A253016 (PARI) for(n=2, 1e9, if(Mod(11, n^2)^(eulerphi(n))==1, print1(n, ", "))) %Y A253016 Cf. A077816, A242958, A242959, A242960, A245529, A241977, A241978. %K A253016 nonn %O A253016 1,1 %A A253016 _Felix Fröhlich_, Dec 26 2014