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A038396 Concatenate first n even numbers in reverse order. 1
2, 42, 642, 8642, 108642, 12108642, 1412108642, 161412108642, 18161412108642, 2018161412108642, 222018161412108642, 24222018161412108642, 2624222018161412108642, 282624222018161412108642, 30282624222018161412108642, 3230282624222018161412108642 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

F. Smarandache conjectures that a(n) is never a perfect power (see link sequence 163 page 80). - Michel Marcus, Mar 03 2014

REFERENCES

Mihaly Bencze [Beneze], L. Tutescu, Some Notions and Questions in Number Theory, Sequence 4.

LINKS

Table of n, a(n) for n=1..16.

Florentin Smarandache, Sequences of Numbers Involved in Unsolved Problems, arXiv:math/0604019 [math.GM], 2006.

FORMULA

a(n) = (2*n)*10^floor(1 + log_10(a(n-1))) + a(n-1), with a(1)=2. - Paolo P. Lava, Jun 19 2008 (may need to be adapted for change in offset)

MAPLE

P:=proc(i) local a, n; a:=2; print(a); for n from 2 by 1 to i do a:=2*n*10^floor(evalf(1+log10(a), 100))+a ; print(a); od; end: P(100); # Paolo P. Lava, Jun 19 2008 (may need to be adapted for change in offset)

MATHEMATICA

Join[{s = 2}, Table[s = FromDigits[Flatten[IntegerDigits[{n, s}]]], {n, 4, 26, 2}]] (* Jayanta Basu, Jul 14 2013 *)

Table[FromDigits[Flatten[IntegerDigits/@Range[2n, 2, -2]]], {n, 20}] (* Harvey P. Dale, Jun 11 2017 *)

PROG

(PARI) a(n) = concat(vector(n, i, Str(2*n - (2*i)+2))); \\ Michel Marcus, Mar 03 2014

CROSSREFS

Sequence in context: A180425 A140170 A318247 * A287328 A276923 A308526

Adjacent sequences:  A038393 A038394 A038395 * A038397 A038398 A038399

KEYWORD

nonn,base,easy

AUTHOR

M. I. Petrescu (mipetrescu(AT)yahoo.com)

EXTENSIONS

More terms from Michel Marcus, Mar 03 2014

STATUS

approved

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Last modified October 23 17:32 EDT 2019. Contains 328373 sequences. (Running on oeis4.)