A179444 - OEIS

%I #8 Jun 11 2019 19:56:08

%S 81,91,121,141,161,201,221,261,301,321,341,351,361,381,391,441,451,

%T 481,501,511,551,561,581,621,651,681,721,741,771,781,801,841,851,861,

%U 871,901,921,931,951,961,981,1001,1041,1081,1101,1111,1121,1141,1161,1191,1211,1221,1241,1251,1261,1281,1331

%N Composite numbers m of the form m = 10k + 1 where k is also composite.

%C Corresponding values of k in A179443.

%H Robert Israel, <a href="/A179444/b179444.txt">Table of n, a(n) for n = 1..10000</a>

%p select(t -> not isprime((t-1)/10) and not isprime(t), [seq(i,i=21..10001,10)]); # _Robert Israel_, Jun 11 2019

%t Select[10#+1&/@Select[Range[100],!PrimeQ[#]&],!PrimeQ[#]&] (* _Harvey P. Dale_, Dec 01 2013 *)

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Jul 14 2010

%E More terms from _Robert Israel_, Jun 11 2019