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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
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
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
See A262300 for more about this problem.
Sequence in context: A262579 A057932 A262578 * A132943 A262576 A362119
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Sep 25 2015
STATUS
approved