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%I #17 Feb 22 2021 21:14:36
%S 2,3,7,5,7,7,9,187
%N a(n) = smallest m >= n such that the decimal concatenation n||n+1||n+2||...||m is prime, or -1 if no such prime exists.
%C These are the values of n+k from A341715. See that entry for more information.
%C See A084559 (the same for nonprime indices) for further information. - _M. F. Hasler_, Feb 22 2021
%C Suppose n > 3. If n == 2 (mod 3), then a(n) == 3 or 5 (mod 6). If n = 0 or 1 (mod 3), then a(n) == 1 (mod 6) (see A341716). - _Chai Wah Wu_, Feb 22 2021
%F a(n) = n iff n is prime, otherwise a(n) = A084559(n). - _M. F. Hasler_, Feb 22 2021
%t Array[Block[{k = #, s = #}, While[! PrimeQ[s], k++; s = FromDigits[IntegerDigits[s]~Join~IntegerDigits[k]]]; k] &, 8, 2] (* _Michael De Vlieger_, Feb 22 2021 *)
%o (PARI) A341717(n)=if(isprime(n), n, A084559(n)) \\ _M. F. Hasler_, Feb 22 2021
%Y Cf. A084559, A140793, A341715, A341716.
%K nonn,base,more
%O 2,1
%A _N. J. A. Sloane_, Feb 22 2021
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