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 1-6 of 6 results.

A071149 Numbers n such that the sum of the first n odd primes (A071148) is prime; analogous to A013916.

Original entry on oeis.org

1, 9, 15, 17, 53, 55, 61, 65, 71, 75, 95, 115, 117, 137, 141, 143, 155, 183, 191, 203, 249, 273, 275, 283, 291, 305, 339, 341, 377, 409, 411, 415, 435, 439, 449, 483, 495, 497, 509, 525, 583, 599, 605, 621, 633, 637, 643, 645, 671, 675, 709, 713, 715, 727
Offset: 1

Views

Author

Labos Elemer, May 13 2002

Keywords

Crossrefs

Programs

Formula

a(n) = pi(A071150(n)). - Charles R Greathouse IV, May 13 2015

A053845 Primes of form prime(1) + ... + prime(k) + 1.

Original entry on oeis.org

3, 11, 29, 59, 101, 239, 569, 1061, 1481, 1721, 4889, 5351, 6871, 22549, 23593, 25801, 29297, 35569, 38239, 41023, 71209, 77137, 87517, 94057, 105541, 120349, 122921, 125509, 128113, 133387, 138869, 141677, 156109, 159073, 165041, 183707
Offset: 1

Views

Author

Enoch Haga, Mar 28 2000

Keywords

Examples

			prime(1) + 1 = 2 + 1 = 3 (prime, thus a(1));
prime(1) + prime(2) + 1 = 2 + 3 + 1 = 6 (nonprime);
prime(1) + prime(2) + prime(3) + 1 = 2 + 3 + 5 + 1 = 11 (prime, thus a(2)); etc. - _Jon E. Schoenfield_, Jan 09 2015
		

Crossrefs

Programs

  • Mathematica
    p=1;lst={};Do[p+=Prime[n];If[PrimeQ[p],AppendTo[lst,p]],{n,7!}];lst (* Vladimir Joseph Stephan Orlovsky, Jun 14 2009 *)
  • PARI
    lista(nn) = {s = 1; for (n=1, nn, s += prime(n); if (isprime(s), print1(s, ", ")););} \\ Michel Marcus, Jan 10 2015
  • UBASIC
    10 x=x+1; 20 if x<>prmdiv(x) then 10; 30 y=x; 40 r=r+y; 50 if r=prmdiv(r) then print r;:p=p+1; 60 if p<100 then 10
    

Formula

a(n) = A007504(A089228(n)) + 1. - Amiram Eldar, Apr 29 2024

A376891 Numbers k such that the sum of the first k lesser of twin primes is a lesser of twin prime.

Original entry on oeis.org

1, 23, 143, 251, 281, 305, 341, 455, 605, 761, 1349, 1613, 2765, 2903, 2981, 3623, 3725, 3923, 4049, 4133, 4745, 5207, 5303, 5489, 5765, 6515, 6611, 7793, 7835, 8153, 8237, 10427, 10697, 11261, 11447, 11627, 11729, 12401, 12701, 13871, 14327, 15359, 15683
Offset: 1

Views

Author

Ilya Gutkovskiy, Oct 08 2024

Keywords

Crossrefs

Programs

  • Maple
    K:= 1: count:= 1: s:= 3: k:= 1:
    for p from 5 by 6 do
      if isprime(p) and isprime(p+2) then
        k:= k+1;
        s:= s+p;
        if s mod 6 = 5 and isprime(s) and isprime(s+2) then
          count:= count+1; K:= K,k;
          if count = 100 then break fi;
    fi fi od:
    K; # Robert Israel, Oct 08 2024
  • Mathematica
    Position[Accumulate[Select[Partition[Prime[Range[200000]],2,1],#[[2]]-#[[1]]==2&][[;;,1]]],?(AllTrue[#+{0,2},PrimeQ]&)]//Quiet//Flatten (* _Harvey P. Dale, Jun 24 2025 *)
  • PARI
    lista(nn) = my(v=select(p->isprime(p+2), primes(nn)), s = vector(#v)); s[1] = v[1]; for (i=2, #v, s[i] = s[i-1]+v[i]); Vec(select(x->(isprime(x) && isprime(x+2)), s, 1)); \\ Michel Marcus, Oct 10 2024

A376892 Numbers k such that the sum of the first k greater of twin primes is a greater of twin prime.

Original entry on oeis.org

1, 45, 105, 675, 987, 1431, 1593, 1677, 1785, 1875, 2037, 2541, 3039, 3045, 3051, 3183, 3267, 3531, 3699, 4113, 4239, 4377, 4443, 5643, 5673, 5709, 6027, 6543, 6615, 6771, 6891, 6915, 6999, 8043, 8109, 8313, 8607, 8739, 10197, 10569, 11103, 11139, 11361, 11787, 12045
Offset: 1

Views

Author

Ilya Gutkovskiy, Oct 08 2024

Keywords

Crossrefs

Programs

  • Maple
    K:= 1: count:= 1: s:= 5: k:= 1:
    for p from 7 by 6 do
      if isprime(p) and isprime(p-2) then
        k:= k+1;
        s:= s+p;
        if s mod 6 = 1 and isprime(s) and isprime(s-2) then
          count:= count+1; K:= K, k;
          if count = 100 then break fi;
    fi fi od:
    K; # Robert Israel, Nov 08 2024
  • PARI
    lista(nn) = my(v=select(p->isprime(p-2), primes(nn)), s = vector(#v)); s[1] = v[1]; for (i=2, #v, s[i] = s[i-1]+v[i]); Vec(select(x->(isprime(x) && isprime(x-2)), s, 1)); \\ Michel Marcus, Oct 10 2024

A264858 Integers k such that A007504(k) + 1 is a square.

Original entry on oeis.org

0, 17, 539, 652, 6420, 350857847
Offset: 1

Views

Author

Altug Alkan, Nov 26 2015

Keywords

Comments

Integers k such that the sum of the first k primes + 1 is a square.
Integers k such that A014284(k+1) is a square.
In A110996, it is commented that a(6) > 250000, if it exists.
a(6) > 50000000, if it exists. - Jon E. Schoenfield, Nov 29 2015

Examples

			a(2) = 17 because A007504(17) + 1 = 440 + 1 = 441 is a square.
		

Crossrefs

Programs

Extensions

a(6) from Jinyuan Wang, Aug 09 2023

A277123 Numbers k such that 1 + Sum_{j=1..k} prime(j)^2 is prime.

Original entry on oeis.org

1, 11, 19, 29, 37, 73, 97, 155, 163, 175, 191, 257, 295, 313, 325, 341, 365, 389, 391, 409, 415, 461, 491, 497, 515, 599, 697, 715, 757, 761, 767, 775, 785, 793, 857, 875, 895, 899, 905, 919, 1099, 1109, 1117, 1139, 1151, 1163, 1225, 1271, 1279, 1295, 1309
Offset: 1

Views

Author

Alex Ratushnyak, Sep 30 2016

Keywords

Crossrefs

Programs

  • Mathematica
    Position[Accumulate[Prime[Range[2000]]^2]+1,?PrimeQ]//Flatten (* _Harvey P. Dale, Sep 07 2019 *)
  • PARI
    lista(nn) = for(n=1, nn, if(isprime(1+sum(i=1, n, prime(i)^2)), print1(n, ", "))); \\ Altug Alkan, Oct 01 2016
  • Python
    import sympy
    sum = p = 1
    for n in range(1,3001):
      while not sympy.isprime(p):  p+=1    # find the n'th prime
      sum += p*p
      p+=1
      if sympy.isprime(sum):  print(n, end=', ')
    
Showing 1-6 of 6 results.