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.

A328019 Positions of 1 in A328018.

Original entry on oeis.org

1, 7, 35, 119, 387, 1050, 2786, 7160, 17157, 39087, 78453, 167183, 344072, 697116, 1310344, 2455274, 4569557, 7758203, 13461761, 23063807, 39017035, 66702580, 106675941, 172270944, 274763136, 437839603, 693741098, 1044076002, 1596344378, 2414009807, 3653875720
Offset: 1

Views

Author

Rens Reus and David A. Corneth, Oct 01 2019

Keywords

Comments

Does a(n+1)/a(n) tend to 1 as n tends to infinity? - Rémy Sigrist, Nov 11 2019

Examples

			A328018 starts like this: 1, 2, 3, 4, 5, 6, 1, 8, 9, 10, 11, 12, 13, 2, 15, 16, 3, 18, 19, 20, 4, 22, 23, 24, 25, 26, 5, 6, 29, 30, 31, 32, 33, 34, 1, 36, 8, 38, 39, 40.
This has 1's in positions 1, 7 and 35. Therefore, 1, 7 and 35 are in the sequence.

Links

Crossrefs

Cf. A092433, A328018.

Programs

  • Mathematica
    With[{s = Select[Range[10^6], Or[Mod[#, 7] == 0, DigitCount[#, 10, 7] > 0] &]}, Nest[Append[#, s[[#[[-1]] ]] ] &, {1}, 12]] (* Michael De Vlieger, Oct 17 2019 *)
  • PARI
    print1 (w=1", "); k=0; for (n=1, oo, if (n%7==0 || setsearch(Set(digits(n)),7), if (w==k++, print1 (w=n", ")))) \\ Rémy Sigrist, Nov 11 2019
  • PARI
    See Links section.

Formula

a(1) = 1; a(n + 1) = A092433(a(n)) for n > 0.

Extensions

More terms from Rémy Sigrist, Nov 11 2019

A328661 If n is the k-th composite number then a(n) = a(k), otherwise a(n) = n.

Original entry on oeis.org

1, 2, 3, 1, 5, 2, 7, 3, 1, 5, 11, 2, 13, 7, 3, 1, 17, 5, 19, 11, 2, 13, 23, 7, 3, 1, 17, 5, 29, 19, 31, 11, 2, 13, 23, 7, 37, 3, 1, 17, 41, 5, 43, 29, 19, 31, 47, 11, 2, 13, 23, 7, 53, 37, 3, 1, 17, 41, 59, 5, 61, 43, 29, 19, 31, 47, 67, 11, 2, 13, 71, 23, 73
Offset: 1

Views

Author

Rémy Sigrist, Oct 24 2019

Keywords

Examples

			a(42) = a(28) = a(18) = a(10) = a(5) = 5.

Links

Crossrefs

See A288469 and A328018 for similar sequences.
Cf. A002808, A006508.

Programs

  • PARI
    k=0; for (n=1, #a=vector(73), print1 (a[n] = if (bigomega(n)>1, a[k++], n) ", "))

Formula

a(n) = 1 iff n belongs to A006508.
Showing 1-2 of 2 results.

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