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 1-3 of 3 results.

A137226 Lesser of twins prime p of A135170(n).

Original entry on oeis.org

29, 41, 71, 101, 149, 197, 239, 269, 311, 419, 461, 521, 599, 617, 641, 809, 821, 827, 881, 1031, 1061, 1151, 1289, 1427, 1607, 1697, 1721, 1871, 2267, 2381, 2657, 2687, 2789, 2969, 3251, 3299, 3527, 3539, 3581, 3821, 3929, 4001, 4049, 4091, 4229, 4241
Offset: 1

Views

Author

Giovanni Teofilatto, Mar 07 2008

Keywords

Crossrefs

Cf. A001359, A135170.

Formula

A135170 INTERSECT A001359. - R. J. Mathar, Jun 28 2010

Extensions

Corrected (71 and 101 inserted) and extended by R. J. Mathar, Jun 28 2010

A151740 Composites that are the sum of two consecutive composite numbers.

Original entry on oeis.org

10, 14, 22, 26, 34, 38, 46, 49, 51, 55, 58, 62, 65, 69, 74, 77, 82, 86, 91, 94, 99, 106, 111, 115, 118, 122, 125, 129, 134, 142, 146, 153, 155, 158, 161, 166, 169, 171, 175, 178, 183, 185, 187, 189, 194, 202, 206, 209, 214, 218, 221, 226, 231, 235, 237, 243, 245
Offset: 1

Views

Author

Claudio Meller, Jun 15 2009

Keywords

Comments

The even terms of this sequence are exactly twice the primes > 3. The odd terms are odd composites c for which the odd integer next to c/2 is not prime. - M. F. Hasler, Jun 16 2009
The English language can be ambiguous! What is meant here is: write down a list of the composite numbers 4,6,8,9,10,12,... Whenever the sum of two adjacent terms is composite, adjoin it to the sequence: 4+6=10, 6+8=14, 10+12=22, ... - N. J. A. Sloane, Nov 26 2019

Links

Crossrefs

Cf. A002808, A151741, A151742, A151743, A151744, A151745, A060254, A060327, A060339, A096785, A096787, A135170. - M. F. Hasler, Jun 16 2009
Cf. A167611 (Essentially the same, except for initial term).

Programs

  • Mathematica
    CompositeNext[n_]:=Module[{k=n+1},While[PrimeQ[k],k++ ];k]; q=6!;lst2={};Do[If[ !PrimeQ[n],c=CompositeNext[n];a2=n+c;If[ !PrimeQ[a2],AppendTo[lst2,a2]]],{n,q}];lst2 (* Vladimir Joseph Stephan Orlovsky, Jun 17 2009 *)
Module[{c=Select[Range[300],CompositeQ],s2},s2=Total/@Partition[c,2,1];Intersection[c,s2]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Nov 27 2019 *)
  • PARI
    isA151740(n)= bittest(n,0) || return(isprime(n/2) && n>6); !isprime(bitor(n\2,1)) && !isprime(n) && n>1 \\ M. F. Hasler, Jun 16 2009
  • Python
    from sympy import isprime, composite
print([totest for k in range(1,92) if not isprime(totest := composite(k) + composite(k+1))]) # Karl-Heinz Hofmann, Feb 06 2024

A151741 Composite which are the sum of three consecutive composite numbers.

Original entry on oeis.org

18, 27, 36, 45, 49, 54, 63, 75, 78, 81, 85, 90, 95, 99, 102, 105, 117, 121, 126, 135, 143, 147, 150, 153, 161, 165, 168, 171, 175, 180, 185, 189, 192, 195, 203, 207, 216, 221, 225, 228, 231, 235, 243, 247, 255, 258, 261, 265, 273, 276, 279, 282, 285, 289, 297
Offset: 1

Views

Author

Claudio Meller, Jun 15 2009

Keywords

Crossrefs

Cf. A151740-A151745, A060254, A060327, A060339, A096785, A096787, A135170.

Programs

  • Mathematica
    Module[{c=Select[Range[300],CompositeQ],s3},s3=Total/@Partition[c,3,1];Intersection[c,s3]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Nov 27 2019 *)
  • PARI
    c1=4;c2=6;for(c3=8,299,isprime(c3) && next;isprime(c1+c2+c3) || print1(c1+c2+c3",");c1=c2;c2=c3) \\ M. F. Hasler, Jun 16 2009
Showing 1-3 of 3 results.

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

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