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 A122785 #12 Apr 19 2022 07:12:13 %S A122785 1,4,8,9,14,21,28,45,56,63,65,105,117,133,153,231,273,292,341,481,511, %T A122785 561,585,645,651,861,949,1001,1016,1105,1106,1281,1288,1365,1387,1417, %U A122785 1541,1649,1661,1729,1736,1785,1905,2044,2047,2169,2465,2501,2696,2701,2821,3145,3171,3201,3277,3605,3641,4005 %N A122785 Nonprimes m such that 8^m == 8 (mod m). %C A122785 Theorem: If both numbers q and 2q-1 are primes and m=q*(2q-1) then 8^m==8 (mod m) (m is in the sequence) iff q is of the form 4k+1. 2701,18721,49141,104653,226801,665281,721801,... are such terms. %p A122785 q:= m-> not isprime(m) and 8&^m mod m = 8 mod m: %p A122785 select(q, [$1..5000])[]; # _Alois P. Heinz_, Apr 19 2022 %t A122785 Select[Range[6000], ! PrimeQ[ # ] && Mod[8^#, # ] == Mod[8, # ] &] %Y A122785 Cf. A020137, A001567. %K A122785 nonn %O A122785 1,2 %A A122785 _Farideh Firoozbakht_, Sep 12 2006 %E A122785 Missing a(8)-a(18) inserted by _Georg Fischer_, Apr 19 2022