login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A242462 a(1) = 10; for n>1, a(n) = (a(n-1)-1) * (smallest odd prime factor of a(n-1)) + 1. 0
10, 46, 1036, 7246, 26248636, 11628145306, 461742021916246, 7849614372576166, 44750651538056716666, 17139499539075722482696, 188534494929832947309646, 69192159639248691662639716, 2144956948816709441541831166, 13721289601580490297543093962506 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Note: this sequence will terminate if a power of 2 occurs.

Conjecture: this sequence is infinite (so it contains no powers of 2). The similar sequence starting with a(1) = 6 terminates after 2 terms: 6 and 16.

Conjecture is true if it turns out that one number in this sequence is one more than a multiple of 41. Any number of the form 2^n-1 that is divisible by 41 is also divisible by 25, which is the square of a prime number greater than 3. Because numbers one less than this sequence's terms are always 9 times a squarefree number, this proves that if a number one less than this sequence is divisible by 41, then this sequence is infinite. - J. Lowell, Jul 17 2017

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

a(1) = 10; 10-1 = 9; 9*5 (smallest odd prime factor of 10) is 45; 45+1=46, so a(2) = 46.

MATHEMATICA

NestList[DeleteCases[FactorInteger[#], w_ /; First@ w == 2][[1, 1]] (# - 1) + 1 &, 10, 13] (* Michael De Vlieger, Jul 18 2017 *)

PROG

(PARI) lista(nn) = {a = 10; for (n=2, nn, olda  = a; print1(a, ", "); a = 1 + (olda-1)*opf(olda); ); } \\ Michel Marcus, May 17 2014

CROSSREFS

Sequence in context: A138041 A219597 A000832 * A253477 A143895 A281767

Adjacent sequences:  A242459 A242460 A242461 * A242463 A242464 A242465

KEYWORD

nonn

AUTHOR

J. Lowell, May 15 2014

EXTENSIONS

a(13)-a(14) and name change from Michel Marcus, May 17 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 25 16:03 EDT 2021. Contains 346291 sequences. (Running on oeis4.)