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Near-repdigit primes with only digits 9 and a single 8 in decimal expansion.
2

%I #9 Mar 29 2020 19:13:07

%S 89,8999,98999,99989,989999,9899999,89999999,99899999,99998999,

%T 99999989,998999999,98999999999,99989999999,999998999999,999999999899,

%U 999999999989,99899999999999,99999899999999,99999999899999,999999899999999,999999999989999,999999999999989

%N Near-repdigit primes with only digits 9 and a single 8 in decimal expansion.

%H Felix Fröhlich, <a href="/A263431/b263431.txt">Table of n, a(n) for n = 1..200</a>

%t Select[Flatten[Table[FromDigits/@Permutations[PadRight[{8},n,9]],{n,15}]],PrimeQ] (* _Harvey P. Dale_, Mar 29 2020 *)

%o (PARI) a002283(n) = 10^n-1

%o a011557(n) = 10^n

%o num(n, k) = a002283(n)-a011557(k)

%o terms(n) = i=0; x=1; while(x > 0, y=x-1; while(y >= 0, if(ispseudoprime(num(x, y)), print1(num(x, y), ", "); i++); if(i==n, break({2})); y--); x++)

%o terms(30) \\ print initial thirty terms

%Y Cf. A020472, A065074, A069661, A105975, A178007.

%K nonn,base,easy

%O 1,1

%A _Felix Fröhlich_, Oct 18 2015

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Last modified September 21 07:45 EDT 2024. Contains 376083 sequences. (Running on oeis4.)