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 1-4 of 4 results.

A176851 Numbers of odd primes between A176100(n) and A176100(n+1).

Original entry on oeis.org

0, 3, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Apr 27 2010

Keywords

Comments

Apart from a(2), a(n) is in {0, 1, 2}. Almost all terms are 0 by the Prime Number Theorem. - Charles R Greathouse IV, May 26 2011

Examples

			a(1)=0 because A176100(1)=0 < 1(nonprime) < A176100(2)=2; a(2)=3 because A175100(2)=2 < 3(odd prime) < 5(odd prime) < 7(odd prime) < 8=A176100(3).

A176393 a(n) = A176100(n) + 1 = 2*A141468(n) + 1.

Original entry on oeis.org

1, 3, 9, 13, 17, 19, 21, 25, 29, 31, 33, 37, 41, 43, 45, 49, 51, 53, 55, 57, 61, 65, 67, 69, 71, 73, 77, 79, 81, 85, 89, 91, 93, 97, 99, 101, 103, 105, 109, 111, 113, 115, 117, 121, 125, 127, 129, 131, 133, 137, 139, 141, 145, 149, 151, 153, 155, 157, 161, 163, 165
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Apr 16 2010

Keywords

Programs

  • Maple
    From R. J. Mathar, Apr 20 2010: (Start)
isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc:
A176100 :=proc(n) if n = 1 then 0; else for a from procname(n-1)+2 by 2 do if not isA001358(a) then return a; end if; end do: end if; end proc:
A176363 := proc(n) 1+A176100(n) ; end proc: seq(A176363(n),n=1..80) ; (End)

Extensions

Corrected (139 inserted) by R. J. Mathar, Apr 20 2010

A178045 Numbers of semiprimes between consecutive even numbers that are not semiprimes.

Original entry on oeis.org

0, 2, 2, 2, 0, 0, 2, 2, 0, 0, 3, 2, 0, 0, 1, 1, 1, 0, 1, 2, 1, 1, 0, 1, 0, 1, 1, 0, 1, 3, 0, 1, 3, 0, 0, 0, 0, 1, 0, 1, 0, 1, 2, 3, 0, 0, 1, 0, 2, 0, 0, 3, 2, 0, 0, 0, 1, 2, 1, 0, 1, 1, 0, 0, 0, 2, 0, 1, 1, 1, 0, 0, 1, 0, 0, 3, 2, 1, 0, 3, 3, 1, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 2, 0, 1, 1, 1, 1, 0, 0, 1
Offset: 1

Views

Author

Juri-Stepan Gerasimov, May 18 2010

Keywords

Comments

Numbers of semiprimes between A176100(n) and A176100(n+1) where A176100 is twice the n-th nonprime numbers.

Examples

			a(1)=0 because 2*A141468(1)=0<2=2*A141468(2); a(2)=2 because 2*A141468(2)=2<4(semiprime)<6(semiprime)<8=2*A141468(3).

Crossrefs

Cf. A001358, A141468, A176851.

Extensions

a(66) and a(67) corrected by R. J. Mathar, May 28 2010

A282671 Twice composite numbers.

Original entry on oeis.org

8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 44, 48, 50, 52, 54, 56, 60, 64, 66, 68, 70, 72, 76, 78, 80, 84, 88, 90, 92, 96, 98, 100, 102, 104, 108, 110, 112, 114, 116, 120, 124, 126, 128, 130, 132, 136, 138, 140, 144, 148, 150, 152, 154, 156, 160, 162, 164, 168, 170, 172, 174
Offset: 1

Views

Author

Alessandro Polcini, Feb 20 2017

Keywords

Comments

Even numbers greater than 2 that do not appear in A001747.

Crossrefs

Cf. A001747, A139270, A176100.

Programs

Formula

a(n) = 2*A002808(n). - R. J. Mathar, Feb 23 2017
a(n) = A139270(n+1). - R. J. Mathar, Feb 25 2017
Showing 1-4 of 4 results.

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