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 1-6 of 6 results.

A175482 a(n) = lesser prime factor of A175461(n).

Original entry on oeis.org

3, 3, 7, 5, 3, 7, 3, 5, 3, 13, 3, 11, 7, 3, 11, 5, 3, 7, 19, 5, 3, 7, 5, 17, 3, 11, 13, 5, 3, 7, 19, 3, 17, 3, 5, 3, 7, 11, 3, 3, 11, 19, 17, 7, 3, 13, 5, 7, 23, 17, 3, 3, 11, 7, 3, 13, 5, 29, 5, 7, 13, 5, 3, 3, 31, 19, 23, 3, 11, 5, 3, 3, 13, 7, 19, 3, 37, 23, 5, 7, 11, 5, 17, 7, 5, 13, 3, 3, 31
Offset: 1

Views

Author

Zak Seidov, May 27 2010

Keywords

Crossrefs

A175483 a(n) = larger prime factor of A175461(n).

Original entry on oeis.org

7, 23, 11, 17, 31, 19, 47, 41, 71, 17, 79, 23, 43, 103, 31, 73, 127, 59, 23, 89, 151, 67, 97, 29, 167, 47, 41, 113, 191, 83, 31, 199, 37, 223, 137, 239, 107, 71, 263, 271, 79, 47, 53, 131, 311, 73, 193, 139, 43, 61, 359, 367, 103, 163, 383, 89, 233, 41, 241, 179, 97, 257
Offset: 1

Views

Author

Zak Seidov, May 27 2010

Keywords

Crossrefs

A178389 Multiples of 3 in A175461.

Original entry on oeis.org

21, 69, 93, 141, 213, 237, 309, 381, 453, 501, 573, 597, 669, 717, 789, 813, 933, 1077, 1101, 1149, 1293, 1317, 1389, 1437, 1461, 1509, 1797, 1821, 1893, 1941, 2157, 2181, 2229, 2253, 2469, 2517, 2589, 2661, 2733, 2757, 2901, 2949, 2973, 3093, 3117, 3189
Offset: 1

Views

Author

Zak Seidov, May 27 2010

Keywords

Crossrefs

Cf. A175461.

Formula

a(n) = 3*A007522(n). [From R. J. Mathar, May 31 2010]

A175463 Numbers k such that 8*k + 5 is semiprime.

Original entry on oeis.org

2, 8, 9, 10, 11, 16, 17, 25, 26, 27, 29, 31, 37, 38, 42, 45, 47, 51, 54, 55, 56, 58, 60, 61, 62, 64, 66, 70, 71, 72, 73, 74, 78, 83, 85, 89, 93, 97, 98, 101, 108, 111, 112, 114, 116, 118, 120, 121, 123, 129, 134, 137, 141, 142, 143, 144, 145, 148, 150, 156, 157, 160
Offset: 1

Views

Author

Zak Seidov, May 24 2010

Keywords

Crossrefs

Cf. A175461 Semiprimes of form 8*n+5.

Programs

  • Magma
    IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [2..200] | IsSemiprime(8*n+5) ]; // Vincenzo Librandi, Dec 13 2010
  • Mathematica
    Select[Range[200],PrimeOmega[8#+5]==2&] (* Harvey P. Dale, Aug 07 2011 *)

Formula

a(n) = (A175461(n) - 5)/8.

A175484 a(n) = (1/2)*(A175482(n)+A175483(n)).

Original entry on oeis.org

5, 13, 9, 11, 17, 13, 25, 23, 37, 15, 41, 17, 25, 53, 21, 39, 65, 33, 21, 47, 77, 37, 51, 23, 85, 29, 27, 59, 97, 45, 25, 101, 27, 113, 71, 121, 57, 41, 133, 137, 45, 33, 35, 69, 157, 43, 99, 73, 33, 39, 181, 185, 57, 85, 193, 51, 119, 35, 123, 93, 55, 131, 217, 221, 37, 45
Offset: 1

Views

Author

Zak Seidov, May 27 2010

Keywords

Crossrefs

A175486 Composite numbers of form 8n+5 with all prime factors of form 8m+5.

Original entry on oeis.org

125, 325, 725, 845, 925, 1325, 1525, 1885, 2197, 2405, 2525, 2725, 3125, 3445, 3725, 3925, 3965, 4205, 4325, 4525, 4901, 4925, 5365, 5725, 6253, 6565, 6725, 6845, 6925, 7085, 7325, 7685, 7925, 8125, 8725, 8845, 8957, 9325, 9685, 9725, 9805, 9925, 10205
Offset: 1

Views

Author

Zak Seidov, May 27 2010

Keywords

Comments

There are no squares and no semiprimes in the sequence.

Examples

			125=5^3, 325=5^2*13, 725=5^2*29.
		

Crossrefs

Cf. A004770 Numbers of form 8n+5, A175461 Semiprimes of form 8n+5, A007521 Primes of form 8n+5.

Programs

  • Mathematica
    Do[nn=8n+5;If[ !PrimeQ[nn]&&{5}==Union[Mod[(fi=First/@FactorInteger[nn]),8]],Print[nn]],{n,2*10^3}]
Showing 1-6 of 6 results.