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A038395 Concatenation of the first n odd numbers in reverse order. 4
1, 31, 531, 7531, 97531, 1197531, 131197531, 15131197531, 1715131197531, 191715131197531, 21191715131197531, 2321191715131197531, 252321191715131197531, 27252321191715131197531, 2927252321191715131197531, 312927252321191715131197531 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) starts with the digits of 2n-1. Indices of prime or probable prime terms are 1,2,37,62,409,...: see also A089922. - M. F. Hasler, Apr 13 2008

If n == 0 (mod 3), so is a(n). - Sergey Pavlov, Mar 29 2017

REFERENCES

Mihaly Bencze [Beneze] and L. Tutescu, Some Notions and Questions in Number Theory, Sequence 3.

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-1)*10^floor(1+log_10(a(n-1))) + a(n-1), with a(1)=1. - Paolo P. Lava, Jun 19 2008

MAPLE

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

MATHEMATICA

Table[FromDigits[Flatten[IntegerDigits/@Join[Reverse[Range[1, n, 2]]]]], {n, 1, 29, 2}] (* Harvey P. Dale, Jun 02 2011 *)

PROG

(PARI) t=""; for( n=1, 10^3, ( t=eval( Str( 2*n-1, t))) & print(n" "t)) \\ M. F. Hasler, Apr 13 2008

(Python)

def a(n): return int("".join(map(str, range(2*n-1, 0, -2))))

print([a(n) for n in range(1, 17)]) # Michael S. Branicky, Jan 31 2021

CROSSREFS

Cf. A089922, A109837, A038394-A038399, A019518, A019519.

Sequence in context: A316457 A278558 A022659 * A261620 A196492 A240420

Adjacent sequences:  A038392 A038393 A038394 * A038396 A038397 A038398

KEYWORD

nonn,base,easy

AUTHOR

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

EXTENSIONS

Edited and extended by M. F. Hasler, Apr 13 2008

Edited by T. D. Noe, Oct 30 2008

STATUS

approved

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Last modified March 1 03:32 EST 2021. Contains 341732 sequences. (Running on oeis4.)