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Numbers k such that prime(k) and prime(k+1) are congruent to 1 (mod 10).
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%I #9 Feb 09 2021 02:29:24

%S 42,53,82,115,125,141,172,177,193,233,279,369,399,431,474,500,575,580,

%T 585,650,651,672,708,737,751,760,795,798,820,841,842,863,873,933,1019,

%U 1031,1099,1112,1166,1178,1225,1245,1266,1312,1352,1436,1463,1479,1505

%N Numbers k such that prime(k) and prime(k+1) are congruent to 1 (mod 10).

%e Prime(42)=181, prime(43)=191. This is the first pair of successive primes both ending with 1.

%t ra=Range[2000];cnd=Mod[Prime[ # ], 10]==Mod[Prime[ #+1], 10]==1&;se=Select[ra, cnd]

%K nonn

%O 1,1

%A _Zak Seidov_, Jun 04 2005