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.

A281437 Primes of the form 25*n^2 + 25*n + 47.

Original entry on oeis.org

47, 97, 197, 347, 547, 797, 1097, 1447, 1847, 2297, 2797, 3347, 3947, 4597, 5297, 6047, 8597, 9547, 11597, 12697, 17597, 18947, 20347, 23297, 24847, 28097, 31547, 33347, 37097, 39047, 41047, 45197, 49547, 51797, 61297, 66347, 68947, 71597, 74297, 77047, 79847
Offset: 1

Views

Author

Waldemar Puszkarz, Oct 05 2017

Keywords

Comments

The first 16 terms correspond to n from 0 to 15, which makes 25*n^2 + 25*n + 47 a prime-generating polynomial (see the link).
This is a prime-generating polynomial of the form s*n^2 + s*n + p, where s=k^2 and p is prime with s and p containing at most two digits. Prime-generating polynomials of this kind arise for k=1,2,3,5,7. This is the case of k=5; it generates most primes in a row out of the prime k's listed, with 12 for k=3,7, and 14 for k=2. See also A005846 and A007635 (k=1), and A048988 (k=2).
All terms are of the form 10m+7, with their next-to-last digits being 4 or 9.

Examples

			197 is a term as it is a prime corresponding to n=2: 25*4 + 25*2 + 47 = 197.
		

Crossrefs

Cf. A000040 (primes), A005846, A007635, A048988, A292578 (similar prime-generating sequences).

Programs

  • Maple
    select(isprime, [seq(25*n^2 + 25*n + 47, n=0..200)]); # Robert Israel, Dec 12 2024
  • Mathematica
    Select[Range[0,100]//25#^2+25#+47&, PrimeQ]
  • PARI
    for(n=0, 100, isprime(p=25*n^2+25*n+47)&& print1(p ", "))

A289839 Primes of the form 8*n^2+8*n+31.

Original entry on oeis.org

31, 47, 79, 127, 191, 271, 367, 479, 607, 751, 911, 1087, 1279, 1487, 1951, 2207, 2767, 3391, 3727, 4079, 4447, 4831, 5231, 5647, 6079, 6991, 9007, 9551, 10111, 10687, 11279, 11887, 12511, 13151, 13807, 14479, 17327, 20431, 21247, 22079, 24671, 26479, 27407
Offset: 1

Views

Author

Waldemar Puszkarz, Oct 06 2017

Keywords

Comments

The first 14 terms correspond to n from 0 to 13, which makes 8*n^2+8*n+31 a prime-generating polynomial (see the link).
This is a prime-generating polynomial of the form c*n^2+c*n+p, where c=2^k (k=0,1,2...) and p is prime with c and p containing at most two digits. Prime-generating polynomials of this kind arise for k=0,1,2,3 - see A005846 and A007635 (k=0), A007639 (k=1), and A048988 (k=2).
All terms are of the form 4m+3. Terms 1 and 4 are Mersenne primes (A000668).

Examples

			79 is a term as it is a prime corresponding to n=2: 8*4+8*2+31=79.
		

Crossrefs

Cf. A000040 (primes), A005846, A007635, A007639, A048988, A281437, A292578 (similar prime-generating sequences).

Programs

  • Mathematica
    Select[Range[0,100]//8#^2+8#+31&, PrimeQ]
  • PARI
    for(n=0, 100, isprime(p=8*n^2+8*n+31)&& print1(p ", "))
Showing 1-2 of 2 results.