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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A373656 a(n) is the n-th prime after the n-th semiprime.

Original entry on oeis.org

5, 11, 17, 19, 31, 37, 47, 53, 61, 67, 79, 83, 89, 101, 103, 113, 131, 137, 149, 151, 157, 173, 179, 191, 199, 211, 227, 233, 239, 241, 257, 263, 269, 271, 293, 313, 331, 337, 347, 349, 353, 359, 373, 383, 389, 409, 419, 421, 431, 433, 449, 461, 463, 467, 487, 499, 509, 521, 547, 557, 563, 577
Offset: 1

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Author

Zak Seidov and Robert Israel, Jun 14 2024

Keywords

Examples

			a(5) = 31 because the 5th semiprime is 14 and the first 5 primes after 14 are 17, 19, 23, 29, 31.
		

Crossrefs

Programs

  • Maple
    N:= 1000: # for terms <= N
    P:= select(isprime, [2, seq(i, i=3..N, 2)]): nP:= nops(P):
    S:= select(t -> numtheory:-bigomega(t)=2, [$1..N]):
    f:= proc(n) local j;
      j:= ListTools:-BinaryPlace(P, S[n]);
      if j + n <= nP then P[j+n] else fail fi
    end proc:
    R:= NULL:
    for i from 1 do
      v:= f(i);
      if v = fail then break fi;
      R:= R, v
    od:
    R;
  • Mathematica
    sp=Select[Range[200],PrimeOmega[#]==2&];Table[NextPrime[sp[[n]],n],{n,62}] (* James C. McMahon, Jul 07 2024 *)

Formula

a(n) = A000040(n + A000720(A001358(n))).
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