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.

A137628 Semiprimes (p+4) associated with last prime in A137626.

Original entry on oeis.org

6, 35, 185, 737, 1781, 8367, 8373, 19277, 175337, 175353, 33952823, 4377722981, 4377723017, 1242030992721, 1242030992727
Offset: 1

Views

Author

Enoch Haga, Jan 30 2008

Keywords

Examples

			a(2)=35 because when p=29 (resp. 31), p+4=33 (resp. 35) and are semiprime (3*3 resp. 5*7).

Crossrefs

Cf. A001358, A137625, A137626, A137627.

Formula

For each p, the semiprime is p + 4.
a(n) = A137626(n) + 4. - Sean A. Irvine, Feb 13 2012

Extensions

a(11) from Sean A. Irvine, Feb 12 2012
a(1) corrected for consistency with change in A137626 by Sean A. Irvine, Jun 21 2018
a(12)-a(15) from Giovanni Resta, Jun 22 2018

A137625 The initial prime in the first set of n consecutive primes for which p+4 is semiprime.

Original entry on oeis.org

2, 29, 173, 709, 1741, 8297, 8297, 19213, 175229, 175229, 33952609, 4377722623, 4377722623, 1242030992173, 1242030992173
Offset: 1

Views

Author

Enoch Haga, Jan 30 2008

Keywords

Comments

Suggested by Carlos Rivera's Puzzle 429 which asks for runs where p+2 is biprime.

Examples

			a(2)=29 because this is the first prime in a run of 2 consecutive primes -- 29 and 31 -- where p+4 is semiprime, i.e., 29+4 and 31+4 are both semiprimes.

Crossrefs

Cf. A001358, A137626, A137627, A137628.

Programs

  • UBASIC
    10 'p+4 is biprime 20 N=1 30 A=3:S=sqrt(N) 40 B=N\A: if B*A=N then N=N+2:goto 30 50 A=A+2: if A<=S then 40 60 C=C+1:O=N+4:D=prmdiv(O):E=O\D 70 if E<>prmdiv(E) or E=1 then C=0:goto 90 80 print C;N;D;E;O: if C>=10 then stop 90 N=N+2:goto 30

Extensions

a(1) corrected and a(11)-a(15) from Giovanni Resta, Jun 22 2018
Example clarified by Harvey P. Dale, Jan 18 2025

A137627 Semiprimes (p+4) associated with first prime in A137625.

Original entry on oeis.org

6, 33, 177, 713, 1745, 8301, 8301, 19217, 175233, 175233, 33952613, 4377722627, 4377722627, 1242030992177, 1242030992177
Offset: 1

Views

Author

Enoch Haga, Jan 30 2008

Keywords

Comments

Some terms may overlap: e.g., k=9 and k=10 both begin with p=175229 where p+4 = 175233.

Examples

			a(2)=33 because if p=29, then p+4 is 33 and semiprime (3*11).

Crossrefs

Cf. A001358, A137625, A137626, A137628.

Formula

For each p, the semiprime is p+4.

Extensions

a(1) corrected by and a(11)-a(15) from Giovanni Resta, Jun 22 2018
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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