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%I #9 Feb 05 2019 10:58:45
%S 20,30,50,60,80,150,160,170,230,250,260,270,280,330,340,350,370,380,
%T 400,440,490,500,520,540,560,570,590,600,650,670,700,730,750,760,910,
%U 940,970,990,1010,1100,1120,1150,1180,1210,1220,1230,1270,1280,1290,1320
%N Two-prime decades.
%H Robert Israel, <a href="/A078499/b078499.txt">Table of n, a(n) for n = 1..10000</a>
%p select(t -> nops(select(isprime, [t+1,t+3,t+7,t+9]))=2, [seq(i,i=10..10^4,10)]); # _Robert Israel_, Feb 05 2019
%o (PARI) decade2(n1,n2) = { if(n1==0,n1=10); forstep(x=n1,n2,10, if(isprime(x+1) && isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x" ");); if(isprime(x+1) && isprime(x+7) && !isprime(x+3) && !isprime(x+9), print1(x" ");); if(isprime(x+1) && isprime(x+9) && !isprime(x+3) && !isprime(x+7), print1(x" ");); if(isprime(x+3) && isprime(x+7) && !isprime(x+1) && !isprime(x+9), print1(x" ");); if(isprime(x+3) && isprime(x+9) && !isprime(x+1) && !isprime(x+7), print1(x" ");); if(isprime(x+7) && isprime(x+9) && !isprime(x+1) && !isprime(x+3), print1(x" ");); ); }
%K easy,nonn,base
%O 1,1
%A _Cino Hilliard_, Jan 04 2003
%E Offset corrected by _Robert Israel_, Feb 05 2019
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