The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A075019

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A075019

a(1) = 1; for n > 1, a(n) = the smallest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.
(history; published version)

#51 by Joerg Arndt at Sun Dec 31 10:12:28 EST 2023

STATUS

editing

approved

#50 by Paolo P. Lava at Sun Dec 31 09:23:34 EST 2023

MAPLE

with(numtheory):

T:=proc(t) local x, y; x:=t; y:=0; while x>0 do x:=trunc(x/10); y:=y+1; od; end:

P:=proc(q) local a, b, n; b:=1; print(1); for n from 2 to q do b:=n+b*10^T(n);

a:=sort([op(divisors(b))]); print(a[2]); od; end: P(100); # Paolo P. Lava, Apr 30 2014

# Alternative:

STATUS

approved

editing

#49 by Joerg Arndt at Thu May 26 09:49:29 EDT 2022

STATUS

reviewed

approved

#48 by Felix Fröhlich at Thu May 26 08:50:59 EDT 2022

STATUS

proposed

reviewed

#47 by Michel Marcus at Thu May 26 08:47:45 EDT 2022

STATUS

editing

proposed

#46 by Michel Marcus at Thu May 26 08:47:39 EDT 2022

CROSSREFS

Cf. A000422, A007908, A075020, A104759, A116504, A116505, A138789, A138790, A138958, A138959, A138960, A138961, A138962.

STATUS

approved

editing

Discussion

Thu May 26

08:47

Michel Marcus: A138958, A138959 : do not belong here

#45 by Jon E. Schoenfield at Sat Mar 02 03:09:09 EST 2019

STATUS

editing

approved

#44 by Jon E. Schoenfield at Sat Mar 02 03:09:07 EST 2019

NAME

a(1) = 1; for n > 1, a(n) = the smallest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.

LINKS

Robert Israel and Robert G. Wilson v, <a href="/A075019/b075019.txt">Table of n, a(n) for n = 1..1000</a> (first 120 terms from Robert Israel)

STATUS

approved

editing

#43 by Alois P. Heinz at Thu Mar 01 14:23:53 EST 2018

STATUS

proposed

approved

#42 by Andrew Howroyd at Thu Mar 01 14:02:55 EST 2018

STATUS

editing

proposed