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 1-3 of 3 results.

A293619 Initial member of 6 consecutive primes a, b, c, d, e, f such that both (f + a)/(d - c) and (e + b)/(d - c) are prime.

Original entry on oeis.org

41, 941, 2269, 2411, 5101, 7193, 7283, 12011, 13159, 18427, 19183, 19961, 25589, 27751, 28579, 31151, 35771, 37313, 41543, 47087, 47939, 50459, 52691, 57251, 58229, 58897, 64279, 64553, 65827, 67121, 67411, 67741, 70853, 78277, 81869, 86353, 88993, 90007, 91253
Offset: 1

Views

Author

K. D. Bajpai, Oct 13 2017

Keywords

Examples

			41 is a term because it is the smallest member of 6 consecutive primes {41, 43, 47, 53, 59, 61} = {a, b, c, d, e, f} and both (f + a)/(d - c) = 17 and (e + b)/(d - c) = 17 are prime.
941 is a term because it is the smallest member of 6 consecutive primes {941, 947, 953, 967, 971, 977} = {a, b, c, d, e, f} and both (f + a)/(d - c) = 137 and (e + b)/(d - c) = 137 are prime.
7193 is a term because it is the smallest member of 6 consecutive primes {7193, 7207, 7211, 7213, 7219, 7229} = {a, b, c, d, e, f} and both (f + a)/(d - c) = 7211 and (e + b)/(d - c) = 7213 are prime.

Crossrefs

Cf. A000040, A292618, A292715, A292743, A293395.

Programs

  • Mathematica
    Select[Partition[Prime@Range[50000], 6, 1], Function[{a, b, c, d, e, f}, And[PrimeQ[(f + a)/(d - c)] && PrimeQ[(e + b)/(d - c)]]] @@ # &][[All, 1]]

A293682 a(n) = least odd number k > 1 such that p = prime(n) is the middle of k consecutive primes which have arithmetic mean p, or 1 if no such k exists.

Original entry on oeis.org

1, 1, 3, 1, 1, 1, 7, 1, 1, 15, 1, 17, 1, 1, 1, 3, 1, 1, 1, 13, 1, 5, 1, 11, 1, 1, 1, 1, 1, 1, 1, 1, 37, 1, 51, 17, 3, 1, 1, 3, 33, 1, 1, 7, 1, 1, 3, 1, 67, 7, 1, 1, 1, 1, 3, 3, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 23, 37, 1, 3, 1, 35, 1, 13, 1, 13, 99, 11, 1
Offset: 1

Views

Author

David A. Corneth, Oct 14 2017

Keywords

Examples

			There are no primes before prime(1) so a(1) = 1.
a(3) = 3 as prime(3) = 5, which is the arithmetic mean of the three consecutive primes {3, 5, 7}.

Crossrefs

Cf. A006562, A034964, A122535, A293395.

Programs

  • PARI
    a(n) = {my(s = pprev = pnxt = p = prime(n), q=1); for(i=1, n-1, pprev = precprime(pprev - 1); pnxt = nextprime(pnxt + 1); s += (pprev + pnxt); q += 2; if(p * q == s, return(q))); return(1)}

A294147 Initial member of 9 consecutive primes {a, b, c, d, e, f, g, h, i} such that (a + b + c)/3, (d + e + f)/3 and (g + h + i)/3 are all prime.

Original entry on oeis.org

63487, 462067, 830777, 847507, 1012159, 1049773, 1250611, 1268747, 1372537, 1372559, 1589657, 1988237, 2567557, 2696569, 2874673, 2967317, 3676111, 3718657, 4196987, 4255067, 4550867, 4669333, 5217911, 5225147, 5716031, 6019553, 6103171, 6725657, 6725731, 7143557
Offset: 1

Views

Author

K. D. Bajpai, Oct 23 2017

Keywords

Examples

			63487 is a term because it is the initial term of 9 consecutive primes {63487, 63493, 63499, 63521, 63527, 63533, 63541, 63559, 63577} = {a, b, c, d, e, f, g, h, i}: the arithmetic mean of three sets, i.e., (a + b + c)/ 3, (d + e + f)/3 and (g + h + i)/3 is prime.

Crossrefs

Cf. A000040, A047948, A122535, A293393, A293395.

Programs

  • Mathematica
    Select[Partition[Prime@ Range[5*10^5], 9, 1], Function[{a, b, c, d, e, f, g, h, i}, AllTrue[{(a + b + c)/3, (d + e + f)/3, (g + h + i)/3}, PrimeQ]] @@ # &][[All, 1]] (* Michael De Vlieger, Oct 23 2017 *)
Showing 1-3 of 3 results.

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