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%I #17 Jun 14 2019 21:50:06
%S 31,41,61,101,131,181,191,241,251,271,311,331,401,461,521,541,601,661,
%T 691,751,761,811,821,881,941,971,1021,1031,1091,1151,1171,1181,1231,
%U 1291,1301,1321,1361,1381,1451,1511,1531,1571,1601,1721,1741,1801,1811
%N Primes ending in 1 such that floor(p/7) ends in a digit > 3.
%C Original definition: Pseudofactor sets of primes ending in 1: 7 greater than 3.
%C These pseudofactors, although not unique sets as their domains seem to overlap, form twelve subsets of primes based on the first digit set {1,3,7,9} when {2,5} are taken away from the prime set. This is one of the four {1}'s sets. There exist {3}'s, {7}'s and {9}'s sets of these same four types.
%C Primes ending in 1 are listed if Mod[floor(a[n]/7), 10]>3, where Mod is the binary "remainder" operator.
%C Primes == 31, 41, 51 or 61 (mod 70). - _Robert Israel_, Jun 14 2019
%H Robert Israel, <a href="/A089721/b089721.txt">Table of n, a(n) for n = 1..10000</a>
%p select(isprime, [seq(seq(70*i+j,j=[31,41,51,61]),i=0..100)]); # _Robert Israel_, Jun 14 2019
%t digits=4*200 a=Delete[Union[Table[If[Mod[Prime[n], 10]==1, Prime[n], 0], {n, 1, digits}]], 1] d2=Dimensions[a][[1]] a7g3=Delete[Union[Table[If[Mod[a[[n]]/7, 10]>3, a[[n]], 0], {n, 1, d2}]], 1]
%t pe1Q[n_]:=Mod[n,10]==1&&Mod[Floor[n/7],10]>3; Select[Prime[Range[ 300]],pe1Q] (* _Harvey P. Dale_, Mar 26 2012 *)
%o (PARI) forprime( p=1,9999, p%10==1 & p\7%10>3 & print1(p",")) \\ _M. F. Hasler_, Apr 06 2009
%K nonn,base
%O 1,1
%A _Roger L. Bagula_, Jan 06 2004
%E Corrected and edited by _M. F. Hasler_, Apr 06 2009
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