A177931 Locations of records in A177930.

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.

Links

Table of n, a(n) for n=1..54.

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

Cf. A177929, A177930, A001359, A174514, A174216, A174217.

Sequence in context: A032533 A062884 A026169 * A060378 A185064 A036975

Adjacent sequences: A177928 A177929 A177930 * A177932 A177933 A177934

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