A219998 - OEIS

%I #6 Dec 08 2012 02:18:28

%S 114,134,135,168,219,249,315,324,348,375,419,431,477,485,513,525,537,

%T 546,561,576,597,641,651,675,693,709,714,727,738,777,798,834,840,848,

%U 849,891,908,936,945,957,999,1002,1005,1038,1041,1081,1082,1092,1134,1176

%N Prime-free decades such that the previous decade is also prime-free.

%C Numbers n such that 10n-9, 10n-7, 10n-3, 10n-1, 10n+1, 10n+3, 10n+7, and 10n+9 are composite.

%H V. Raman, <a href="/A219998/b219998.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) ~ n.

%F a(n) = A216288(n) + 1.

%o (PARI) for(i=2, 1200, if(isprime(10*i-9)==0&&isprime(10*i-7)==0&&isprime(10*i-3)==0&&isprime(10*i-1)==0&&isprime(10*i+1)==0&&isprime(10*i+3)==0&&isprime(10*i+7)==0&&isprime(10*i+9)==0, print1(i", ")))

%Y Cf. A190639, A032352.

%Y Cf. A216288 (lower decade).

%K nonn,base

%O 1,1

%A _V. Raman_, Dec 07 2012