The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A271720 a(1)=1; for n>1, define a sequence {b(m), m >= 1} by b(1)=n b(2)=13, and b(m) = A020639(b(m-2)) + A006530(b(m-1)); then a(n) is the number of terms in that sequence before the first of the infinite string of 4s. 1
 8, 13, 15, 13, 4, 13, 12, 13, 15, 13, 4, 13, 16, 13, 15, 13, 12, 13, 15, 13, 15, 13, 4, 13, 4, 13, 15, 13, 8, 13, 12, 13, 15, 13, 4, 13, 12, 13, 15, 13, 4, 13, 8, 13, 15, 13, 12, 13, 12, 13, 15, 13, 12, 13, 4, 13, 15, 13, 4, 13, 8, 13, 15, 13, 4, 13, 12, 13, 15, 13, 8, 13, 11, 13, 15, 13, 12, 13 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Note that the majority of the terms (every other term, initially) are equal to b(2), which is 13. This happens with several other values of b(2) less than 20. Many other values for b(2) have been tested, and it seems that for all b(2) < 100000000, a(n) < 20. Records 8, 13, 15, 16, 19, 20, 24, ... occur at 1, 2, 3, 13, 349, 3919, 55633, ... LINKS Antti Karttunen, Table of n, a(n) for n = 1..65537 EXAMPLE n = 6; the sequence is: 6, 13, 15, 18, 6, 5, 7, 12, 10, 7, 9, 10, 8, 4, 4, 4, ... There are 13 terms before the first of the infinite 4s; a(6) = 13. For n = 55633 the sequence is: 55633, 13, 55646, 27836, 6961, 6963, 7172, 166, 85, 19, 24, 22, 13, 15, 18, 6, 5, 7, 12, 10, 7, 9, 10, 8, 4, 4, 4, ... . As the first 4 comes as the 25th term, a(55633) = 24. - Antti Karttunen, Oct 01 2018 MATHEMATICA Table[ Clear[h]; h[1]=x; h[2]=13; h[n_]:=FactorInteger[h[n-1]][[-1, 1]]+FactorInteger[h[n-2]][[1, 1]]; Position[Array[h, 100], 4][[1, 1]]-1, {x, 1, 100}] (*This only works for x≠4*) PROG (PARI) A006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1); \\ From A006530 A020639(n) = if(1==n, n, factor(n)[1, 1]); A271720(n) = { my(up=1001, bvec = vector(up), m=1); bvec[1] = n; bvec[2] = 13; for(n=3, oo, bvec[n] = A020639(bvec[n-2])+A006530(bvec[n-1]); if(4==bvec[n], return(n-1))); }; \\ Antti Karttunen, Oct 01 2018 CROSSREFS Sequence in context: A253775 A168137 A252458 * A243436 A214412 A080361 Adjacent sequences:  A271717 A271718 A271719 * A271721 A271722 A271723 KEYWORD nonn AUTHOR Cody M. Haderlie, Apr 12 2016 STATUS approved

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

Last modified May 28 16:37 EDT 2022. Contains 354119 sequences. (Running on oeis4.)