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 A275978 Numbers n such that (101*10^n + 1)/3 is prime. 0
 1, 4, 6, 12, 34, 54, 60, 61, 73, 148, 349, 552, 649, 967, 1044, 2521, 4501, 5721, 6133, 9052, 9880, 16126, 16215, 19146, 61770 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that the digits 33 followed by n-1 occurrences of the digit 6 followed by the digit 7 is prime (see Example section). a(26) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 336w7. EXAMPLE 4 is in this sequence because (101*10^4 + 1)/3 = 336667 is prime. Initial terms and primes associated: a(1) = 1, 337; a(2) = 4, 336667; a(3) = 6, 33666667; a(4) = 12, 33666666666667; a(5) = 34, 336666666666666666666666666666666667, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(101*10^# + 1)/3] &] PROG (PARI) isok(n) = isprime((101*10^n + 1)/3); \\ Michel Marcus, Aug 16 2016 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A027070 A087785 A081198 * A242211 A073167 A060202 Adjacent sequences:  A275975 A275976 A275977 * A275979 A275980 A275981 KEYWORD nonn,more AUTHOR Robert Price, Aug 15 2016 STATUS approved

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Last modified August 8 05:25 EDT 2020. Contains 336290 sequences. (Running on oeis4.)