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 A262577 Concatenation of the numbers from 1 to n but omitting 7. 0
 1, 12, 123, 1234, 12345, 123456, 1234568, 12345689, 1234568910, 123456891011, 12345689101112, 1234568910111213, 123456891011121314, 12345689101112131415, 1234568910111213141516, 123456891011121314151617, 12345689101112131415161718, 1234568910111213141516171819, 123456891011121314151617181920 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are only three primes among the first 98 terms: 123456891011, 12345689101112131415161718192021222324252627282930313233343536373839, and 12345689101112131415161718192021222324252627282930313233343536373839\ 40414243444546474849505152535455565758596061626364566676869707172737\ 475767778798081828384858687. Does the sequence contain any other primes? Yes, Pari reports the next (probable) prime after appending 13097; it has 54655 digits. - Bill McEachen, Oct 13 2015 LINKS FORMULA (a(n) - a(n-1)) mod 2 = 0 only for n=7. - Altug Alkan, Oct 15 2015 MATHEMATICA DeleteDuplicates@ Table[If[n >= 7, FromDigits@ Delete[Flatten[IntegerDigits /@ Range[n + 1]], 7], FromDigits@ Flatten[IntegerDigits /@ Range@ n]], {n, 19}] (* Michael De Vlieger, Oct 13 2015 *) CROSSREFS Cf. A007908, A262299, A262571-A262582. See A262300 for more about this problem. Sequence in context: A262579 A057932 A262578 * A132943 A262576 A262575 Adjacent sequences:  A262574 A262575 A262576 * A262578 A262579 A262580 KEYWORD nonn,base AUTHOR N. J. A. Sloane, Sep 25 2015 STATUS approved

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Last modified March 30 08:56 EDT 2020. Contains 333125 sequences. (Running on oeis4.)