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%I #14 Feb 24 2024 15:09:29
%S 1,2,4,8,10,16,20,24,29,33,36,46,76,99,108,132,179,213,217,251,286,
%T 397,431,439,445,471,535,658,677,702,780,889,1227,1296,1388,1395,1430,
%U 1438,1624,1817,2082,2396,2423,2978,3133,3138,3432,3511,3699,3838,4024,4104,4589,4930
%N Locations of records in A177930.
%C Or: positions m for which A177929(m)-1 and A177929(m)+1 are twin primes.
%p A020639 := proc(n) numtheory[factorset](n) ; min(op(%)) ; end proc:
%p 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:
%p A177930 := proc(n) d1 := A020639(A177929(n)-1) ; d2 := A020639(A177929(n)+1) ; min(d1,d2) ; end proc:
%p read("transforms") ; L := [seq(A177930(n),n=1..1300)] ; RECORDS(L)[2] ; # _R. J. Mathar_, May 31 2010
%t lpf[n_] := FactorInteger[n][[1, 1]];
%t b[n_] := b[n] = If[n == 1, 4, b[n-1] + lpf[b[n-1]^2-1]-1];
%t Position[Table[b[n], {n, 1, 1000}], k_ /; PrimeQ[k-1] && PrimeQ[k+1]] // Flatten (* _Jean-François Alcover_, Feb 24 2024 *)
%Y Cf. A177929, A177930, A001359, A174514, A174216, A174217.
%K nonn
%O 1,2
%A _Vladimir Shevelev_, May 15 2010
%E Extended by _R. J. Mathar_, May 31 2010
%E More terms from _Jean-François Alcover_, Feb 24 2024
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