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

Author

Vladimir Shevelev, May 15 2010

Keywords

• nonn

Comments

Or: positions m for which A177929(m)-1 and A177929(m)+1 are twin primes.

Crossrefs

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

Programs

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 *)

Extensions

Extended by R. J. Mathar, May 31 2010

More terms from Jean-François Alcover, Feb 24 2024