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 1-2 of 2 results.

A034387 Sum of primes <= n.

Original entry on oeis.org

0, 2, 5, 5, 10, 10, 17, 17, 17, 17, 28, 28, 41, 41, 41, 41, 58, 58, 77, 77, 77, 77, 100, 100, 100, 100, 100, 100, 129, 129, 160, 160, 160, 160, 160, 160, 197, 197, 197, 197, 238, 238, 281, 281, 281, 281, 328, 328, 328, 328, 328, 328, 381, 381, 381, 381, 381
Offset: 1

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Keywords

Comments

Also sum of all prime factors in n!.
For large n, these numbers can be closely approximated by the number of primes < n^2. For example, the sum of primes < 10^10 = 2220822432581729238. The number of primes < (10^10)^2 or 10^20 = 2220819602560918840. This has a relative error of 0.0000012743... - Cino Hilliard, Jun 08 2008
Equals row sums of triangle A143537. - Gary W. Adamson, Aug 23 2008
Partial sums of A061397. - Reinhard Zumkeller, Mar 21 2014

Crossrefs

This is a lower bound on A287881.

Programs

  • Haskell
    a034387 n = a034387_list !! (n-1)
    a034387_list = scanl1 (+) a061397_list
    -- Reinhard Zumkeller, Mar 21 2014
    
  • Maple
    a:= proc(n) option remember; `if`(n<1, 0,
          a(n-1)+`if`(isprime(n), n, 0))
        end:
    seq(a(n), n=1..60);  # Alois P. Heinz, Jun 29 2022
  • Mathematica
    s=0; Table[s=s+n*Boole[PrimeQ[n]],{n,100}] (* Zak Seidov, Apr 11 2011 *)
    Accumulate[Table[If[PrimeQ[n],n,0],{n,60}]] (* Harvey P. Dale, Jul 25 2016 *)
  • PARI
    a(n)=sum(i=1,primepi(n),prime(i)) \\ Michael B. Porter, Sep 22 2009
    
  • PARI
    a=0;for(k=1,100,print1(a=a+k*isprime(k),", ")) \\ Zak Seidov, Apr 11 2011
    
  • PARI
    a(n) = if(n <= 1, return(0)); my(r=sqrtint(n)); my(V=vector(r, k, n\k)); my(L=n\r-1); V=concat(V, vector(L, k, L-k+1)); my(T=vector(#V, k, V[k]*(V[k]+1)\2)); my(S=Map(matrix(#V,2,x,y,if(y==1,V[x],T[x])))); forprime(p=2, r, my(sp=mapget(S,p-1), p2=p*p); for(k=1, #V, if(V[k] < p2, break); mapput(S, V[k], mapget(S,V[k]) - p*(mapget(S,V[k]\p) - sp)))); mapget(S,n)-1; \\ Daniel Suteu, Jun 29 2022
    
  • Python
    from sympy import isprime
    from itertools import accumulate
    def alist(n): return list(accumulate(k*isprime(k) for k in range(1, n+1)))
    print(alist(57)) # Michael S. Branicky, Sep 18 2021

Formula

From the prime number theorem a(n) has the asymptotic expression: a(n) ~ n^2 / (2 log n). - Dan Fux (dan.fux(AT)OpenGaia.com), Apr 07 2001
a(n) = A158662(n) - 1. a(p) - a(p-1) = p, for p = primes (A000040), a(c) - a(c-1) = 0, for c = composite numbers (A002808). - Jaroslav Krizek, Mar 23 2009
a(n) = n^2/(2 log n) + O(n^2 log log n/log^2 n). - Vladimir Shevelev and Charles R Greathouse IV, May 29 2014
Conjecture: G.f.: Sum_{i>0} Sum_{j>=i} Sum_{k>=j|i-j+k is prime} x^k. - Benedict W. J. Irwin, Mar 31 2017
a(n) = (n+1)*A000720(n) - A046992(n). - Ridouane Oudra, Sep 18 2021
a(n) = A007504(A000720(n)). - Ridouane Oudra, Feb 22 2022
a(n) = Sum_{p<=n, p prime} p. - Wesley Ivan Hurt, Dec 31 2023

A361690 Number of primes in the interval [2^n, 2^n + n].

Original entry on oeis.org

0, 2, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 0, 0, 3, 4, 0, 3, 0, 2, 1, 1, 3, 0, 0, 1, 0, 2, 1, 5, 1, 1, 2, 1, 0, 1, 2, 2, 2, 2, 1, 1, 2, 3, 0, 1, 3, 1, 0, 0, 1, 2, 2, 0, 3, 0, 2, 0, 0, 1, 3, 0, 1, 3, 0, 1, 2, 3, 1, 2, 2, 1, 1, 2, 3, 2, 4, 2, 2, 1, 2, 4, 1, 3, 0, 3, 2, 1, 2, 0
Offset: 0

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Author

Jean-Marc Rebert, Mar 20 2023

Keywords

Examples

			In the interval [2^1, 2^1 + 1] there are 2 primes (2 and 3). So a(1) = 2.
		

Crossrefs

Programs

  • Maple
    a:= n-> nops(select(isprime, [$2^n..2^n+n])):
    seq(a(n), n=0..100);  # Alois P. Heinz, Mar 20 2023
  • Mathematica
    Array[PrimePi[2^# + #] - PrimePi[2^# - 1] &, 50, 0] (* Michael De Vlieger, Mar 27 2023 *)
  • PARI
    a(n)=#primes([2^n,2^n+n])
    
  • Python
    from sympy import isprime
    def A361690(n): return sum(1 for p in range((1<Chai Wah Wu, Mar 27 2023

Formula

From Alois P. Heinz, Mar 20 2023: (Start)
a(n) = pi(2^n+n) - pi(2^n-1), pi = A000720.
a(n) = A143537(2^n+n,2^n-1). (End)
Showing 1-2 of 2 results.