cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A244435 a(n) is the smallest number m such that 2*k*m - 1 is composite for all k, 0 < k < n+1.

Original entry on oeis.org

5, 13, 13, 62, 73, 73, 89, 118, 118, 118, 118, 118, 236, 926, 959, 959, 959, 959, 959, 959, 1063, 1474, 1474, 1474, 1667, 1667, 6118, 8249, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 9098, 35573, 35573, 35573, 57448, 57448, 57448, 57448, 57448, 57448, 57448
Offset: 1

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Author

Farideh Firoozbakht, Jul 19 2014

Keywords

Comments

a(2)=a(3)=13, a(5)=a(6)=73, ... a(29)=a(30)=...=a(43)=9098, ... . A244436 gives numbers k such that a(k) is not in the set {a(k-1), a(k+1)}.

Links

Crossrefs

Cf. A124516, A244433, A244436.

Programs

  • Maple
    M:= 0: R:= NULL:
for m from 2 while M < 100 do
  for i from 0 while not isprime(2*i*m-1) do od:
  if i-1 > M then R:= R, m$(i-1-M); M:= i-1; fi;
od:
R; # Robert Israel, May 03 2021
  • PARI
    isok(n, m) = for(k=1, n, my(x=2*k*m-1); if ((x==1) || isprime(x), return(0))); return (1);
a(n) = my(m=1); while(!isok(n, m), m++); m; \\ Michel Marcus, May 04 2021
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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