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.

Previous Showing 11-15 of 15 results.

A127493 Indices k such that the coefficient [x^1] of the polynomial Product_{j=0..4} (x-prime(k+j)) is prime.

Original entry on oeis.org

1, 5, 8, 9, 22, 29, 45, 49, 60, 69, 87, 89, 90, 107, 114, 124, 125, 131, 134, 138, 145, 156, 171, 183, 188, 191, 203, 204, 207, 212, 219, 255, 261, 290, 298, 303, 329, 330, 343, 344, 349, 354, 378, 397, 398, 400, 403, 454, 456, 466, 474, 515, 549, 560, 570, 578
Offset: 1

Views

Author

Artur Jasinski, Jan 16 2007

Keywords

Comments

A fifth-order polynomial with 5 roots which are the five consecutive primes from prime(k) onward is defined by Product_{j=0..4} (x-prime(k+j)). The sequence is a catalog of the cases where the coefficient of its linear term is prime.
Indices k such that e4(prime(k), prime(k+1), ..., prime(k+4)) is prime, where e4 is the elementary symmetric polynomial summing all products of four variables. - Charles R Greathouse IV, Jun 15 2015

Examples

			For k=2, the polynomial is (x-3)*(x-5)*(x-7)*(x-11)*(x-13) = x^5-39*x^4+574*x^3-3954*x^2+12673*x-15015, where 12673 is not prime, so k=2 is not in the sequence.
For k=5, the polynomial is x^5-83*x^4+2710*x^3-43490*x^2+342889*x-1062347, where 342889 is prime, so k=5 is in the sequence.

Links

Crossrefs

Cf. A001043, A034961, A034963, A034964, A127333-A127343, A127345-A127351, A037171, A034962, A034965, A082246, A082251, A070934, A006094, A046301-A046303, A046324-A046327, A127489, A127491, A127492, A024449.

Programs

  • Maple
    isA127493 := proc(k)
    local x,j ;
    mul( x-ithprime(k+j),j=0..4) ;
    expand(%) ;
    isprime(coeff(%,x,1)) ;
end proc:
A127493 := proc(n)
    option remember ;
    if n = 1 then
        1;
    else
        for a from procname(n-1)+1 do
            if isA127493(a) then
                return a;
            end if;
        end do:
    end if;
end proc:
seq(A127493(n),n=1..60) ; # R. J. Mathar, Apr 23 2023
  • Mathematica
    a = {}; Do[If[PrimeQ[(Prime[x] Prime[x + 1]Prime[x + 2]Prime[x + 3] + Prime[x] Prime[x + 2]Prime[x + 3]Prime[x + 4] + Prime[x] Prime[x + 1]Prime[x + 3]Prime[x + 4] + Prime[x] Prime[x + 1]Prime[x + 2]Prime[x + 4] + Prime[x + 1] Prime[x + 2]Prime[x + 3]Prime[x + 4])], AppendTo[a, x]], {x, 1, 1000}]; a
  • PARI
    e4(v)=sum(i=1,#v-3, v[i]*sum(j=i+1,#v-2, v[j]*sum(k=j+1,#v-1, v[k]*vecsum(v[k+1..#v]))))
pr(p, n)=my(v=vector(n)); v[1]=p; for(i=2,#v, v[i]=nextprime(v[i-1]+1)); v
is(n,p=prime(n))=isprime(e4(pr(p,5)))
v=List(); n=0; forprime(p=2,1e4, if(is(n++,p), listput(v,n))); Vec(v) \\ Charles R Greathouse IV, Jun 15 2015

Extensions

Definition and comment rephrased and examples added by R. J. Mathar, Oct 01 2009

A179007 Sum of 3 consecutive composite odd numbers.

Original entry on oeis.org

45, 61, 73, 85, 95, 107, 119, 133, 145, 155, 163, 175, 185, 197, 209, 221, 233, 243, 253, 263, 271, 279, 287, 299, 315, 331, 343, 351, 357, 363, 369, 377, 387, 397, 409, 419, 429, 435, 445, 455, 467, 475, 485, 495, 505, 515, 523, 535, 545, 555, 561, 571, 585, 599
Offset: 1

Views

Author

Vladimir Joseph Stephan Orlovsky, Jan 07 2011

Keywords

Examples

			9+15+21=45, 15+21+25=61, 21+25+27=73,..

Crossrefs

Cf. A034962, A034965, A082246

Programs

  • Mathematica
    t=Select[Range[2, 200], OddQ[#] && ! PrimeQ[#] &]; Plus @@@ Partition[t, 3, 1]

A179012 Primes that are the sum of three consecutive composite odd numbers.

Original entry on oeis.org

61, 73, 107, 163, 197, 233, 263, 271, 331, 397, 409, 419, 467, 523, 571, 599, 677, 691, 757, 827, 839, 883, 929, 997, 1039, 1051, 1063, 1097, 1123, 1153, 1163, 1171, 1187, 1223, 1231, 1291, 1301, 1367, 1433, 1493, 1523, 1531, 1571, 1619, 1627, 1637, 1667, 1693, 1783
Offset: 1

Views

Author

Vladimir Joseph Stephan Orlovsky, Jan 07 2011

Keywords

Examples

			15+21+25=61, 21+25+27=73, 33+35+39=107.

Links

Crossrefs

Cf. A034962, A034965, A082246, A179007.

Programs

  • Mathematica
    lst={};Do[If[!PrimeQ[n],s=n;k=1,Continue[]];If[!PrimeQ[n+2],s+=n+2;k=2;q=2,If[!PrimeQ[n+4],s+=n+4;k=2;q=4,If[!PrimeQ[n+6],s+=n+6;k=2;q=6]]];If[!PrimeQ[n+q+2],s+=n+q+2;k=3;q+=2,If[!PrimeQ[n+q+4],s+=n+q+4;k=3;q+=4,If[!PrimeQ[n+q+6],s+=n+q+6;k=3;q+=6]]];If[PrimeQ[s],AppendTo[lst,s]],{n,9,6!,2}];lst
nn=1001;With[{compodd=Complement[Range[9,nn,2],Prime[Range[ PrimePi[ nn]]]]}, Select[ Total/@ Partition[compodd,3,1],PrimeQ]] (* Harvey P. Dale, Dec 09 2012 *)

A125270 Coefficient of x^2 in polynomial whose zeros are 5 consecutive primes starting with the n-th prime.

Original entry on oeis.org

1358, 3954, 10478, 22210, 43490, 78014, 129530, 206650, 324350, 466270, 621466, 853742, 1132130, 1436690, 1870850, 2388050, 2886370, 3440410, 4133410, 4904906, 5926654, 7195670, 8425430, 9792950, 11040910, 12098990, 13917898, 16097810
Offset: 1

Views

Author

Artur Jasinski, Jan 16 2007

Keywords

Comments

Sums of all distinct products of 3 out of 5 consecutive primes, starting with the n-th prime; value of 3rd elementary symmetric function on the 5 consecutive primes.

Crossrefs

Cf. A001043, A034961, A034963, A034964, A127333, A127334, A127335, A127336, A127337, A127338, A127339, A127340, A127341, A127342, A127343, A127345, A127346, A127347, A127348, A127349, A127351, A037171, A034962, A034965, A082246, A082251, A070934, A006094, A046301, A046302, A046303, A046324, A046325, A046326, A046327, A127489.

Programs

  • Mathematica
    a = {}; Do[AppendTo[a, (Prime[x] Prime[x + 1] Prime[x + 2] + Prime[x] Prime[x + 1] Prime[x + 3] + Prime[x] Prime[x + 1] Prime[x + 4] + Prime[x] Prime[x + 2] Prime[x + 3] + Prime[x] Prime[x + 2] Prime[x + 4] + Prime[x] Prime[x + 3] Prime[x + 4] + Prime[x + 1] Prime[x + 2] Prime[x + 3] + Prime[x + 1] Prime[x + 2] Prime[x + 4] + Prime[x + 1] Prime[x + 3] Prime[x + 4] + Prime[x + 2] Prime[x + 3] Prime[x + 4])], {x, 1, 100}]; a
fcp[{p_,q_,r_,s_,t_}]:=p*q(r+s+t)+(p+q)r(s+t)+(p+q+r)s*t; fcp/@Partition[ Prime[ Range[40]],5,1] (* Harvey P. Dale, Sep 05 2014 *)

Formula

Let p = Prime(n), q = Prime(n+1), r = Prime(n+2), s = Prime(n+3) and t = Prime(n+4). Then a(n) = p q (r+s+t) + (p + q) r (s + t) + (p + q + r) s t.

Extensions

Edited and corrected by Franklin T. Adams-Watters, Jan 23 2007

A341338 a(n) is the smallest prime that is simultaneously the sum of 2n-1, 2n+1 and 2n+3 consecutive primes.

Original entry on oeis.org

83, 311, 55813, 437357, 1219789, 8472193, 9496853, 6484103, 2166953, 37296143, 12671599, 13432571, 14968909, 145616561, 732092831, 220872569, 1381099933, 93482633, 4142423, 87030017, 3193060007, 736535783, 6390999871, 280886077, 464341303, 268231657, 686836817, 9000046663
Offset: 1

Views

Author

Zak Seidov, Apr 25 2021

Keywords

Examples

			For n = 1: 83 = 23 + 29 + 31 = 11 + 13 + 17 + 19 + 23, and 83 is the smallest prime that is the sum of 1, 3 and 5 consecutive primes, so a(1) = 83.

Crossrefs

Cf. A034962, A034965, A082246, A082251, A127340, A127341, A161612.

Programs

  • Mathematica
    Array[(k=1;
While[(i=Select[Intersection@@((Total/@Subsequences[Prime@Range@Prime[k++],{#}])&/@{2#-1,2#+1,2#+3}),PrimeQ])=={}];First@i)&,4] (* Giorgos Kalogeropoulos, Apr 26 2021 *)
Previous Showing 11-15 of 15 results.

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

Content is available under The OEIS End-User License Agreement.