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.

Showing 1-4 of 4 results.

A122984 Smallest positive composite number, relatively prime to n, such that a(n)+n is also composite.

Original entry on oeis.org

8, 25, 22, 21, 4, 49, 8, 25, 16, 39, 4, 65, 8, 25, 34, 9, 4, 77, 6, 49, 4, 27, 4, 25, 8, 9, 8, 27, 4, 91, 4, 25, 16, 15, 4, 49, 8, 25, 10, 9, 4, 143, 6, 21, 4, 9, 4, 77, 6, 27, 4, 25, 4, 65, 8, 9, 8, 27, 4, 143, 4, 15, 22, 21, 4, 25, 8, 9, 8, 51, 4, 49, 4, 21, 16, 9, 4, 55, 6, 39, 4, 9, 4, 85
Offset: 1

Views

Author

Franklin T. Adams-Watters, Sep 22 2006

Keywords

Comments

Does not include every composite number; in particular, 12 is not present. If a(n) = 12, gcd(n,12) = 1, but then one of n+4 and n+8 is divisible by 3.

Crossrefs

Equals A122985(n) - n. Cf. A096076.

A122985 Smallest composite number greater than n, relatively prime to n, such that a(n)-n is also composite.

Original entry on oeis.org

9, 27, 25, 25, 9, 55, 15, 33, 25, 49, 15, 77, 21, 39, 49, 25, 21, 95, 25, 69, 25, 49, 27, 49, 33, 35, 35, 55, 33, 121, 35, 57, 49, 49, 39, 85, 45, 63, 49, 49, 45, 185, 49, 65, 49, 55, 51, 125, 55, 77, 55, 77, 57, 119, 63, 65, 65, 85, 63, 203, 65, 77, 85, 85, 69, 91, 75, 77, 77
Offset: 1

Views

Author

Franklin T. Adams-Watters, Sep 22 2006

Keywords

Crossrefs

Equals A122984(n) + n. Cf. A096076.

Programs

  • Mathematica
    scn[n_]:=Module[{k=n+1},While[!CompositeQ[k]||!CoprimeQ[n,k] || !CompositeQ[ k-n],k++];k]; Array[scn,70] (* Harvey P. Dale, Jul 26 2019 *)

A076772 Even numbers n representable as the sum of 2 coprime odd composites.

Original entry on oeis.org

34, 44, 46, 52, 58, 62, 64, 68, 74, 76, 82, 86, 88, 92, 94, 98, 100, 102, 104, 106, 112, 114, 116, 118, 122, 124, 128, 130, 134, 136, 142, 144, 146, 148, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 182, 184, 186, 188, 190, 192, 194
Offset: 0

Views

Author

Jon Perry, Nov 14 2002

Keywords

Comments

As the comment in A096076 indicates, 210 is the largest even number not in this sequence. - Franklin T. Adams-Watters, Sep 07 2006

Examples

			34=25+9

Crossrefs

Cf. A096076.

Programs

  • PARI
    v=vector(5000); vc=1; forstep (n=9,300,2, if (isprime(n),continue, forstep (j=9,300,2,if (gcd(n,j)==1, if (isprime(j),continue,x=n+j; fl=true; for (i=1,vc,if (v[i]==x,fl=false; break)); if (fl==true,v[vc]=x; vc++)))))); print(vc); v=vecsort(vecextract(v,concat("1..",vc-1)))

A197640 Numbers not representable as the sum of two coprime, squarefree, composite, positive integers.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 56, 58, 60, 62, 63, 64, 66, 70, 72, 75, 78, 80, 82, 84, 88, 90, 96, 100, 102, 105, 108, 110, 114, 120, 126, 130, 132, 138, 140, 144, 150, 156, 168, 180, 190, 204, 210, 240, 270, 330, 420
Offset: 1

Views

Author

Jason Holland, Oct 16 2011

Keywords

Comments

a(87) = 420 is probably the last term.

Crossrefs

Cf. A197629, A096076.

Programs

  • PARI
    is(n)=for(k=6,n\2,if(gcd(k,n-k)==1&&!isprime(k)&&!isprime(n-k)&&issquarefree(k)&&issquarefree(n-k),return(0)));1 \\ Charles R Greathouse IV, Oct 18 2011
Showing 1-4 of 4 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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