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.

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A156778 a(n) = n*A007504(n)/2 = n*(sum of first n primes)/2.

Original entry on oeis.org

0, 1, 5, 15, 34, 70, 123, 203, 308, 450, 645, 880, 1182, 1547, 1967, 2460, 3048, 3740, 4509, 5396, 6390, 7476, 8701, 10051, 11556, 13250, 15093, 17064, 19194, 21460, 23895, 26660, 29616, 32802, 36159, 39830, 43686, 47804, 52193, 56823, 61740
Offset: 0

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Author

M. F. Hasler, Feb 21 2009

Keywords

Comments

For n>0, the sum of the first n primes, A007504(n), has the opposite parity of n (since both increase by an odd amount, and A007504(n)=2 for n=1).

Crossrefs

Cf. A007504, A156780.

Programs

  • PARI
    vector(80,n,n--;sum(i=1,n,prime(i))*n)/2
  • PARI
    a(n) = n*vecsum(primes(n))/2 \\ Jason Yuen, Feb 03 2025

Formula

a(n) = A156780(prime(n))/2, where prime(n) = A000040(n) is the n-th prime.
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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