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.

A088176 Primes such that the previous two primes are a twin prime pair.

Original entry on oeis.org

7, 11, 17, 23, 37, 47, 67, 79, 107, 113, 149, 157, 191, 197, 211, 233, 251, 277, 293, 317, 353, 431, 439, 467, 541, 577, 607, 631, 647, 673, 821, 827, 839, 863, 887, 1031, 1039, 1061, 1069, 1097, 1163, 1237, 1283, 1297, 1307, 1327, 1433, 1459, 1487, 1493, 1613
Offset: 1

Views

Author

Zak Seidov, Sep 22 2003

Keywords

Comments

Primes p such that prevprime(p) - 2 is prime. - Irina Gerasimova, Jun 28 2013

Links

Crossrefs

Cf. A088175.

Programs

Extensions

More terms from Ray Chandler, Sep 25 2003
Definition clarified by Irina Gerasimova, Jun 28 2013

A144550 Largest non-twin prime < n-th and (n+1)-th twin primes.

Original entry on oeis.org

2, 23, 37, 53, 67, 97, 131, 173, 223, 233, 263, 277, 307, 337, 409, 457, 509, 563, 593, 613, 631, 653, 797, 853, 877, 1013, 1039, 1087, 1129, 1223, 1259, 1283, 1297, 1307, 1423, 1447, 1471, 1601, 1613, 1663, 1693, 1709, 1783, 1867, 1913, 1993, 2017, 2069
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Dec 31 2008

Keywords

Links

Crossrefs

Cf. A077800, A088175.

Programs

  • Maple
    isA077800 := proc(n) isprime(n) and ( isprime(n+2) or isprime(n-2)) ; end proc:
isA007510 := proc(n) isprime(n) and not isA077800(n) ; end proc:
isA144550 := proc(n) isA007510(n) and isA077800( nextprime(n)) ; end proc:
for n from 2 to 2500 do if isA144550(n) then printf("%d,",n) ; end if; end do: # R. J. Mathar, May 01 2010
  • Mathematica
    Module[{nn=400,tps},tps=Union[Flatten[Select[Partition[Prime[Range[nn]],2,1], #[[2]]-#[[1]] == 2&]]];Complement[NextPrime[#,-1]&/@tps,tps]] (* Harvey P. Dale, Jun 23 2022 *)

Formula

{A007510(k): nextprime(A007510(k)) in A077800}. - R. J. Mathar, May 01 2010

Extensions

Corrected (1993 inserted) by R. J. Mathar, May 01 2010

A227031 Odd primes such that the previous prime is not the larger part of a twin prime pair.

Original entry on oeis.org

3, 5, 13, 19, 29, 31, 41, 43, 53, 59, 61, 71, 73, 83, 89, 97, 101, 103, 109, 127, 131, 137, 139, 151, 163, 167, 173, 179, 181, 193, 199, 223, 227, 229, 239, 241, 257, 263, 269, 271, 281, 283, 307, 311, 313, 331, 337, 347, 349, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421
Offset: 1

Views

Author

Irina Gerasimova, Jun 28 2013

Keywords

Comments

This is the complement of A088176 in the set of odd primes. - R. J. Mathar, Jul 04 2013

Examples

			a(1) = 3 because 3 is prime and prevprime(3) - 2 = 2 - 2 = 0 is not prime,
a(2) = 5 because 5 is prime and prevprime(5) - 2 = 3 - 2 = 1 is not prime,
a(3) = 13 because 13 is prime and prevprime(13) - 2 = 11 - 2 = 9 is composite.

Links

Crossrefs

Cf. A088175, A088176.

Programs

  • Mathematica
    Select[Prime[Range[2, 100]], Not[PrimeQ[NextPrime[#, -1] - 2]] &] (* Alonso del Arte, Jul 04 2013 *)
  • PARI
    is(n)=n>2 && !isprime(precprime(n-2)-2) && isprime(n) \\ Charles R Greathouse IV, Mar 18 2014

Formula

a(n) ~ prime(n) ~ n log n. - Charles R Greathouse IV, Jun 28 2013
Showing 1-3 of 3 results.

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