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 A228625 Primes of the form abcabc..abca. 4

%I #15 Aug 29 2013 23:16:21

%S 1021,1031,1051,1061,1091,1151,1171,1181,1201,1231,1291,1301,1321,

%T 1361,1381,1451,1471,1481,1511,1531,1571,1601,1621,1721,1741,1801,

%U 1811,1831,1861,1871,1901,1931,1951,3023,3083,3163,3203,3253,3313,3323,3343,3373,3413

%N Primes of the form abcabc..abca.

%C The sequence appears to be infinite.

%H Shyam Sunder Gupta and Charles R Greathouse IV, <a href="/A228625/b228625.txt">Table of n, a(n) for n = 1..829</a> (all terms with up to 1000 digits; first 500 from Gupta)

%e a(2)= 1031 is in the sequence because it is a prime of the form abca.

%t s[n_]:=Select[Union@Flatten@Table[FromDigits@Flatten@Join[IntegerDigits@Table[b,{n}],{IntegerDigits@Floor[b/100]}],{b,100,999}],PrimeQ];Array[s,2]//Flatten

%o (PARI) for(k=1,9,b=10^(3*k+1);for(n=1,999,if(isprime(t=b*n\999), print1(t", ")))) \\ _Charles R Greathouse IV_, Aug 29 2013

%K nonn,base

%O 1,1

%A _Shyam Sunder Gupta_, Aug 28 2013

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Last modified May 30 18:38 EDT 2024. Contains 372971 sequences. (Running on oeis4.)