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 1-5 of 5 results.

A171994 Members of A171697 that have exactly three prime factors.

Original entry on oeis.org

245, 325, 343, 425, 475, 637, 665, 715, 805, 833, 845, 847, 925, 1001, 1025, 1045, 1075, 1175, 1265, 1331, 1463, 1475, 1505, 1519, 1645, 1675, 1705, 1729, 1771, 1805, 1855, 1885, 1955, 2023, 2035, 2057, 2075, 2093, 2107, 2185, 2197, 2225
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Jan 21 2010

Keywords

Extensions

Corrected, edited and extended by Editors of the OEIS, Mar 29 2010

A172015 Numbers of the form 6*k-+1 such that 6*k-1=prime and 6*k+1=nonprime.

Original entry on oeis.org

23, 25, 47, 49, 53, 55, 83, 85, 89, 91, 113, 115, 131, 133, 167, 169, 173, 175, 233, 235, 251, 253, 257, 259, 263, 265, 293, 295, 317, 319, 353, 355, 359, 361, 383, 385, 389, 391, 401, 403, 443, 445, 449, 451, 467, 469, 479, 481, 491, 493, 503, 505, 509, 511
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Jan 22 2010

Keywords

Crossrefs

A171688 U A171697 U A172015 U A172016 = A007310.

Programs

  • Mathematica
    Select[Table[{6k-1, 6k+1}, {k, 1, 100}], PrimeQ[ #[[1]] ] && !PrimeQ[ #[[2]] ]&] // Flatten (* Jean-François Alcover, Nov 24 2016 *)

Extensions

Entries checked by R. J. Mathar, Apr 14 2010

A172016 Numbers of the form 6*k-+1 such that 6*k-1=nonprime and 6*k+1=prime.

Original entry on oeis.org

35, 37, 65, 67, 77, 79, 95, 97, 125, 127, 155, 157, 161, 163, 209, 211, 221, 223, 275, 277, 305, 307, 329, 331, 335, 337, 365, 367, 371, 373, 377, 379, 395, 397, 407, 409, 437, 439, 455, 457, 485, 487, 497, 499, 539, 541, 545, 547, 575, 577, 605, 607, 611
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Jan 22 2010

Keywords

Links

Crossrefs

A171688 U A171697 U A172015 U A172016 = A007310.

Programs

  • Mathematica
    Select[#+{-1,1}&/@(6Range[200]),CompositeQ[#[[1]]]&&PrimeQ[#[[2]]]&]// Flatten (* Harvey P. Dale, Nov 19 2019 *)

Extensions

Entries checked by R. J. Mathar, Apr 14 2010

A172017 Twin semiprimes: nonprimes of the form 6*k-+1 where 6*k-+1 are both semiprime.

Original entry on oeis.org

119, 121, 143, 145, 185, 187, 203, 205, 215, 217, 287, 289, 299, 301, 413, 415, 515, 517, 527, 529, 533, 535, 551, 553, 581, 583, 695, 697, 779, 781, 791, 793, 815, 817, 869, 871, 893, 895, 899, 901, 959, 961, 1055, 1057, 1079, 1081, 1133, 1135, 1139
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Jan 22 2010

Keywords

Links

Crossrefs

Cf. A001358 (semiprimes), A171697 (twin natural nonprimes).

Programs

  • Mathematica
    Select[{#-1,#+1}&/@(6*Range[200]),PrimeOmega[#]=={2,2}&]//Flatten (* Harvey P. Dale, Nov 14 2018 *)

Extensions

Corrected (623,625 removed) by R. J. Mathar, May 22 2010

A171995 Twin natural nonprimes with nonprime number of prime factors.

Original entry on oeis.org

1, 625, 1715, 1925, 2125, 2875, 2975, 3575, 3773, 4165, 4225, 4235, 4625, 5125, 5375, 5425, 5635, 5831, 5875, 5915, 6517, 6625, 7007, 7225, 7315, 7375, 7595, 7625, 7735, 7889, 7975, 8075, 8225, 8281, 8855, 8875, 9025, 9425, 9775, 9875, 10045, 10075
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Jan 21 2010

Keywords

Comments

Intersection of A171697 and A167175. - R. J. Mathar, Mar 29 2010

Examples

			a(1)=1(without prime factors), a(2)=625(=5*5*5*5), a(3)=1715(=5*7*7*7).

Crossrefs

Cf. A167175, A171697.

Programs

  • PARI
    isA171995(n)=n>0&!isprime(n)&((n%6==1&!isprime(n-2))||(n%6==5&!isprime(n+2)))&!isprime(bigomega(n))

Extensions

Edited and extended by Charles R Greathouse IV, Mar 29 2010
Showing 1-5 of 5 results.

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

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