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 A108821 Primes such that the outer 2 digits are n and n+1 and all inner digits are 4, where 0 < n < 9. 1
 647, 24443, 84449, 644447, 24444443, 64444444447, 2444444444443, 84444444444449, 2444444444444444444444444444443, 84444444444444444444444444444444444449 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..27 FORMULA a(x) = 10^(x+1)*n+floor(10^x*4/9)*10+n+1. Output if a(x) is prime. MATHEMATICA Select[Sort[Flatten[Table[FromDigits[Join[{n}, PadRight[{}, m, 4], {n+1}]], {n, 8}, {m, 40}]]], PrimeQ] (* Harvey P. Dale, Mar 17 2019 *) PROG (PARI) n10np1(n) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+floor(10^x*4/9)*10+k+1; if(isprime(y), print1(y", ")) ) ) } CROSSREFS Sequence in context: A250989 A187434 A046020 * A345702 A035885 A114827 Adjacent sequences:  A108818 A108819 A108820 * A108822 A108823 A108824 KEYWORD easy,nonn,base AUTHOR Cino Hilliard, Jul 11 2005 STATUS approved

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Last modified August 19 20:38 EDT 2022. Contains 356231 sequences. (Running on oeis4.)