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A290984 First n-digit number to appear twice in a row in the decimal expansion of e. 2
6, 95, 427, 1828, 34619, 507629, 7342911, 21958718 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

18281828 appears in e before any 1-digit, 2-digit, or 3-digit number appears twice in a row.

a(n) starts at positions 31, 49, 97, 2, 112869, 5005575, 1561314, 69682897, ... - Bobby Jacobs, Sep 05 2017

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

a(1) = 6 because 6 is the first 1-digit number to appear twice in a row in the decimal expansion of e = 2.718281828459045235360287471352(66)...

MATHEMATICA

With[{s = Rest@ First@ RealDigits[N[E, 10^5]]}, Keys@ Merge[#, Identity] &@ Table[TakeSmallest[#, 1] &@ Sort[Map[#[[1, 1]] &, DeleteCases[#, {}]]] &@ Map[SequenceCases[#, {a_, b_} /; b == a + n] &, KeyMap[FromDigits, PositionIndex@ Partition[s, n, 1]]], {n, 4}]] (* Michael De Vlieger, Aug 16 2017 *)

(* or *)

s = First@ RealDigits[E, 10, 51*^5]; Table[p = Partition[s, k, 1]; FromDigits @@ p[[ Select[ Range[ Length@p - k], p[[#]] == p[[#+k]] &, 1]]], {k, 7}] (* much faster, Giovanni Resta, Sep 05 2017 *)

CROSSREFS

Cf. A001113, A288291, A290977.

Sequence in context: A180260 A184981 A058465 * A326436 A243802 A119627

Adjacent sequences:  A290981 A290982 A290983 * A290985 A290986 A290987

KEYWORD

base,more,nonn

AUTHOR

Bobby Jacobs, Aug 16 2017

EXTENSIONS

a(6)-a(8) from Giovanni Resta, Sep 05 2017

STATUS

approved

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Last modified July 22 16:43 EDT 2019. Contains 325225 sequences. (Running on oeis4.)