A381074 Numbers k such that k, k+2 and k+4 are all terms in A380846.

10820236, 24069388, 27802288, 39297580, 50717488, 56362960, 73070224, 97339504, 103605964, 112209580, 112526032, 140053564, 145315600, 155790124, 156415084, 158877232, 184667248, 185979664, 188913004, 189225484, 189541936, 224435536, 281740396, 292406380, 314388112

Offset

1,1

Comments

Numbers k such that A380845(k) = 2*k, A380845(k+2) = 2*(k+2), and A380845(k+4) = 2*(k+4).

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Mathematica

f[n_] := Module[{h = DigitCount[n, 2, 1]}, DivisorSum[n, # &, DigitCount[#, 2, 1] == h &] == 2*n]; seq[lim_] := Module[{q = Table[False, {6}], s = {}}, q[[1 ;; 4]] = f /@ Range[4]; Do[q[[5 ;; 6]] = f /@ Range[k, k + 1]; If[q[[1]] && q[[3]] && q[[5]], AppendTo[s, k - 4]]; If[q[[2]] && q[[4]] && q[[6]], AppendTo[s, k - 3]]; q[[1 ;; 4]] = q[[3 ;; 6]], {k, 5, lim, 2}]; s]; seq[11000000]

Prog

(PARI) is1(k) = {my(h = hammingweight(k)); sumdiv(k, d, d*(hammingweight(d) == h)) == 2*k; }
list(lim) = {my(q1 = is1(1), q2 = is1(2), q3 = is1(3), q4 = is1(4), q5, q6); forstep(k = 5, lim, 2, q5 = is1(k); q6 = is1(k+1); if(q1 && q3 && q5, print1(k-4, ", ")); if(q2 && q4 && q6, print1(k-3, ", ")); q1 = q3; q2 = q4; q3 = q5; q4 = q6); }

Crossrefs

Subsequence of A380846 and A381073.

Cf. A380845.

Sequence in context: A344634 A071370 A203942 * A251488 A214245 A233621

Adjacent sequences: A381071 A381072 A381073 * A381075 A381076 A381077

Keyword

nonn,base

Author

Amiram Eldar, Feb 13 2025

Status

approved