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%I #7 Apr 13 2020 13:19:21
%S 90,110,120,140,180,210,240,290,300,360,390,410,420,450,470,480,550,
%T 580,630,660,680,690,710,720,740,770,780,790,800,810,830,860,870,900,
%U 920,930,950,960,980,1000,1020,1040,1050,1080,1110,1160,1170,1190,1200,1240
%N One-prime decades.
%C The year 2003 is the only prime year in the 2000 decade.
%t Select[10*Range[200],PrimePi[#+10]-PrimePi[#]==1&] (* _Harvey P. Dale_, Apr 13 2020 *)
%o (PARI) decade1(n1,n2) = { forstep(x=n1,n2,10, if(isprime(x+1) && !isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x" ");); if(isprime(x+3) && !isprime(x+1) && !isprime(x+7) && !isprime(x+9), print1(x" ");); if(isprime(x+7) && !isprime(x+1) && !isprime(x+3) && !isprime(x+9), print1(x" ");); if(isprime(x+9) && !isprime(x+1) && !isprime(x+3) && !isprime(x+7), print1(x" ");); ); }
%K easy,nonn,base
%O 0,1
%A _Cino Hilliard_, Jan 04 2003
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