Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #7 Jul 28 2022 03:31:59
%S 1,2,4,5,181,324,1253,252649,69789901
%N Numbers k such that prime(k) is congruent to sigma(k) (mod k), where prime(n) denotes the n-th prime.
%C a(10) > 10^12. - _Donovan Johnson_, Mar 14 2010
%e prime(5) = 11 is congruent to sigma(5) = 6 (mod 5), so 5 is in the sequence.
%t Select[ Range[ 1, 10^5 ], Mod[ DivisorSigma[ 1, # ], # ] == Mod[ Prime[ # ], # ] & ]
%K nonn,hard,more
%O 1,2
%A _Joseph L. Pe_, Jan 11 2002
%E a(9) from _Donovan Johnson_, Mar 14 2010