A192504 Ludic nonprime numbers.

1, 25, 77, 91, 115, 119, 121, 143, 161, 175, 209, 221, 235, 247, 265, 287, 301, 329, 341, 361, 377, 407, 415, 437, 445, 475, 481, 493, 497, 517, 527, 535, 553, 565, 581, 595, 625, 667, 685, 697, 703, 707, 749, 775, 791, 803, 805, 835, 841, 851, 865, 893, 913

Offset

1,2

Comments

The sequence appears to have linear growth with ratio a(n)/n ~ 1.73... - M. F. Hasler, Nov 04 2024

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Formula

A010051(a(n))*(1-A192490(a(n))) = 1.

Mathematica

a3309[nmax_] := a3309[nmax] = Module[{t = Range[2, nmax], k, r = {1}}, While[Length[t] > 0, k = First[t]; AppendTo[r, k]; t = Drop[t, {1, -1, k}]]; r];
ludicQ[n_, nmax_] /; 1 <= n <= nmax := MemberQ[a3309[nmax], n];
terms = 1000;
f[nmax_] := f[nmax] = Select[Range[nmax], ludicQ[#, nmax] && ! PrimeQ[#]&] // PadRight[#, terms]&;
f[nmax = terms];
f[nmax = 2 nmax];
While[f[nmax] != f[nmax/2], nmax = 2 nmax];
seq = f[nmax] (* Jean-François Alcover, Dec 10 2021, after _Ray CHandler_ in A003309 *)

Prog

(Haskell)
a192504 n = a192504_list !! (n-1)
a192504_list = filter ((== 0) . a010051) a003309_list
(PARI) A192504(maxn, bflag=0)={my(Vw=vector(maxn, x, x+1), Vl=Vec([1]), vwn=#Vw, i, vj, L=List());
while(vwn>0, i=Vw[1]; Vl=concat(Vl, [i]);
      Vw=vector((vwn*(i-1))\i, x, Vw[(x*i+i-2)\(i-1)]); vwn=#Vw);
kill(Vw); vwn=#Vl;
for(j=1, vwn, vj=Vl[j]; if(!isprime(vj), listput(L, vj))); kill(Vw); vwn=#L;
if(bflag, for(i=1, vwn, print(i, " ", L[i]))); if(!bflag, return(Vec(L)));
} \\ Anatoly E. Voevudko, Feb 28 2016

Crossrefs

Intersection of A018252 and A003309.

Cf. A010051, A192490.

Cf. A002808.

Sequence in context: A042230 A189642 A221309 * A363635 A033658 A080699

Adjacent sequences: A192501 A192502 A192503 * A192505 A192506 A192507

Keyword

nonn

Author

Reinhard Zumkeller, Jul 05 2011

Status

approved