cp's OEIS Frontend

A087441 Numbers k such that for every prime divisor p of k, p-1 divides k-1.

%I A087441 #10 Apr 23 2021 05:10:51
%S A087441 1,2,3,4,5,7,8,9,11,13,16,17,19,23,25,27,29,31,32,37,41,43,45,47,49,
%T A087441 53,59,61,64,67,71,73,79,81,83,89,97,101,103,107,109,113,121,125,127,
%U A087441 128,131,137,139,149,151,157,163,167,169,173,179,181,191,193,197,199,211
%N A087441 Numbers k such that for every prime divisor p of k, p-1 divides k-1.
%C A087441 This sequence contains all powers of prime numbers (A000961). The remaining numbers form the sequence A087442.
%H A087441 Amiram Eldar, <a href="/A087441/b087441.txt">Table of n, a(n) for n = 1..10000</a>
%e A087441 45 is in A087441 because its prime divisors are 3 and 5 and 3-1 = 2 as well as 5-1 = 4 divide 45-1 = 44.
%t A087441 Join[{1},Select[Range[2,300],And@@Divisible[#-1,FactorInteger[#][[All, 1]]-1]&]] (* _Harvey P. Dale_, Aug 07 2019 *)
%o A087441 (GAP) for i in [1..225] do if i = 1 or IsSubset (DivisorsInt(i-1), Set (FactorsInt (i)) - 1) then Print (i, ", "); fi; od;
%Y A087441 Cf. A000961, A087442.
%K A087441 easy,nonn
%O A087441 1,2
%A A087441 _Jens Voß_, Sep 04 2003