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.

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A325571 Composite numbers n that have no divisor d > 1 such that A048720(A065621(d),n/d) = n.

Original entry on oeis.org

15, 25, 27, 39, 51, 55, 57, 63, 69, 77, 81, 85, 87, 91, 95, 99, 111, 115, 117, 119, 121, 123, 125, 141, 143, 145, 147, 159, 169, 171, 175, 177, 183, 185, 187, 201, 203, 205, 207, 209, 213, 215, 219, 221, 231, 235, 237, 243, 245, 247, 249, 253, 255, 261, 265, 267, 275, 285, 287, 289, 291, 295, 299, 301, 303, 305, 319, 321
Offset: 1

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Author

Antti Karttunen, May 10 2019

Keywords

Crossrefs

Intersection of A002808 and A325570.

Programs

  • PARI
    A048720(b,c) = fromdigits(Vec(Pol(binary(b))*Pol(binary(c)))%2, 2);
    A065621(n) = bitxor(n-1,n+n-1);
    isA325571(n) = ((n>1)&&!isprime(n)&&fordiv(n,d,if(A048720(A065621(n/d),d)==n,return(d==n))));

A325572 Numbers n that have divisor d > 1 such that A048720(A065621(d),n/d) = n.

Original entry on oeis.org

2, 4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 21, 22, 24, 26, 28, 30, 32, 33, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 49, 50, 52, 54, 56, 58, 60, 62, 64, 65, 66, 68, 70, 72, 74, 75, 76, 78, 80, 82, 84, 86, 88, 90, 92, 93, 94, 96, 98, 100, 102, 104, 105, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 129, 130, 132, 133
Offset: 1

Views

Author

Antti Karttunen, May 10 2019

Keywords

Comments

Equally, numbers n such that there exists natural numbers t > 1 and u >= 1, for which A048720(t,u) = n and A065620(t)*u = n.

Crossrefs

Cf. A048720, A065620, A065621, A325570 (complement).
Union of A005843 (without zero) and A325573 (odd terms).

Programs

Showing 1-2 of 2 results.