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A177931
Locations of records in A177930.
4
1, 2, 4, 8, 10, 16, 20, 24, 29, 33, 36, 46, 76, 99, 108, 132, 179, 213, 217, 251, 286, 397, 431, 439, 445, 471, 535, 658, 677, 702, 780, 889, 1227, 1296, 1388, 1395, 1430, 1438, 1624, 1817, 2082, 2396, 2423, 2978, 3133, 3138, 3432, 3511, 3699, 3838, 4024, 4104, 4589, 4930
OFFSET
1,2
COMMENTS
Or: positions m for which A177929(m)-1 and A177929(m)+1 are twin primes.
MAPLE
A020639 := proc(n) numtheory[factorset](n) ; min(op(%)) ; end proc:
A177929 := proc(n) option remember; if n = 1 then 4; else d1 := A020639(procname(n-1)-1) ; d2 := A020639(procname(n-1)+1) ; procname(n-1)+min(d1, d2) -1; end if; end proc:
A177930 := proc(n) d1 := A020639(A177929(n)-1) ; d2 := A020639(A177929(n)+1) ; min(d1, d2) ; end proc:
read("transforms") ; L := [seq(A177930(n), n=1..1300)] ; RECORDS(L)[2] ; # R. J. Mathar, May 31 2010
MATHEMATICA
lpf[n_] := FactorInteger[n][[1, 1]];
b[n_] := b[n] = If[n == 1, 4, b[n-1] + lpf[b[n-1]^2-1]-1];
Position[Table[b[n], {n, 1, 1000}], k_ /; PrimeQ[k-1] && PrimeQ[k+1]] // Flatten (* Jean-François Alcover, Feb 24 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, May 15 2010
EXTENSIONS
Extended by R. J. Mathar, May 31 2010
More terms from Jean-François Alcover, Feb 24 2024
STATUS
approved