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 1-2 of 2 results.

A371191 Nonsquare terms of A349062.

Original entry on oeis.org

1372, 465125, 4879688, 6272006419, 3533294646441, 405211279147678088
Offset: 1

Views

Author

Amiram Eldar, Mar 14 2024

Keywords

Comments

There are no more terms below 10^18.
There are 276407671 terms of A349062 below 10^18, of them only 6 are nonsquare numbers.

Examples

			1372 = 2^2 * 7^3 is a term since it is a term of A349062 (the gap to the next powerful number, 1444, is 72, which is a record) and it is not a square.
		

Crossrefs

Intersection of A000037 and A349062.
Cf. A227297.

Programs

  • Mathematica
    seq[max_] := Module[{pows = Union[Flatten[Table[i^2*j^3, {j, 1, Surd[max, 3]}, {i, 1, Sqrt[max/j^3]}]]], gapmax = 0, gap, s = {}}, Do[gap = pows[[k+1]] - pows[[k]]; If[gap > gapmax, gapmax = gap; If[!IntegerQ[Sqrt[pows[[k]]]], AppendTo[s, pows[[k]]]]], {k, 1, Length[pows] - 1}]; s]; seq[10^10]
  • PARI
    lista(mx) = {my(s = List(), gap, gapmax = 0); for(j = 1, sqrtnint(mx, 3), for(i = 1, sqrtint(mx\j^3), listput(s, i^2 * j^3))); s = Set(s); for(k = 1, #s - 1, gap = s[k+1] - s[k]; if(gap > gapmax, gapmax = gap; if(!issquare(s[k]), print1(s[k], ", "))));}

A272714 Numbers n such that both n and n+1 are Achilles numbers (A052486).

Original entry on oeis.org

5425069447, 11968683934831, 28821995554247, 48689748233307
Offset: 1

Views

Author

Felix Fröhlich, May 12 2016

Keywords

Comments

Any term of the sequence is also a term of A227297, but the converse is not always true. The smallest term of A227297 where the converse fails is A227297(1) = 12167. Do any other such numbers exist?

Examples

			5425069447 = 7^3 * 41^2 * 97^2 and 5425069448 = 2^3 * 26041^2. Since every prime factor of 5425069447 and 5425069448 is repeated, both numbers are Achilles numbers (A052486) and since the two numbers differ by 1, i.e., the value of A247246 at the index of 5425069447 in A052486 is 1, 5425069447 is a term of the sequence.
		

Crossrefs

Programs

  • PARI
    is(n) = vecmin(factor(n)[, 2]) > 1 && vecmin(factor(n+1)[, 2]) > 1 && !ispower(n) && !ispower(n+1)
Showing 1-2 of 2 results.