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 1-4 of 4 results.

A077673 Duplicate of A071255.

Original entry on oeis.org

2, 3, 5, 7, 11, 17, 29, 46, 74, 119, 195, 319, 521, 859, 1407, 2315, 3810, 6267, 10303
Offset: 1

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Author

Keywords

A072415 a(1) = 2; a(n) = a(n-1)-th even nontotient number.

Original entry on oeis.org

2, 26, 182, 878, 3626, 13508, 46922, 155156, 494468, 1529590, 4615074, 13633310, 39548078, 112918434, 317920082, 883996002
Offset: 1

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Author

Labos Elemer, Jun 17 2002

Keywords

Crossrefs

Programs

  • Mathematica
    a = Table[0, {10^6}]; Do[b = EulerPhi[n]/2; If[b < 10^6 + 1, a[[b]] = 1], {n, 1, 2 10^7}]; b = Select[ Range[10^6], a[[ # ]] == 0 &]; c = 1; Do[ Print[c]; c = 2b[[c]], {n, 0, 8}]

Formula

a(3)=182 is the 26th = a(2)-th term in A005277.

Extensions

Edited by Robert G. Wilson v, Jun 20 2002
a(11)-a(16) from Donovan Johnson, Oct 29 2010

A072416 a(1) = 2; a(n) = half of the a(n-1)-th even nontotient number.

Original entry on oeis.org

2, 13, 49, 149, 373, 835, 1727, 3383, 6341, 11419, 19966, 34067, 56967, 93578, 151313, 241281, 379934, 591413, 910879, 1389289, 2099905, 3147743, 4682362, 6914234, 10141072, 14779023, 21408820, 30837491, 44179913, 62974570, 89329823
Offset: 1

Views

Author

Labos Elemer, Jun 17 2002

Keywords

Crossrefs

Programs

  • Mathematica
    a = Table[0, {10^6}]; Do[b = EulerPhi[n]/2; If[b < 10^6 + 1, a[[b]] = 1], {n, 1, 2 10^7}]; b = Select[ Range[10^6], a[[ # ]] == 0 &]; c = 2; Do[ Print[c]; c = b[[c]], {n, 0, 17}]

Formula

a(5) = 373 = 746/2, where 746 is the a(4) = 149th term in A005277.

Extensions

Edited by Robert G. Wilson v, Jun 20 2002
a(18)-a(31) from Donovan Johnson, Oct 29 2010

A356398 a(1) = 4, and for any n > 1, a(n+1) is the a(n)-th squarefree number.

Original entry on oeis.org

4, 5, 6, 7, 10, 14, 21, 33, 53, 85, 138, 222, 366, 599, 985, 1613, 2651, 4357, 7169, 11795, 19401, 31913, 52487, 86347, 142021, 233615, 384277, 632091, 1039741, 1710305, 2813358, 4627790, 7612435, 12521926, 20597674, 33881799, 55733298, 91677666, 150803687
Offset: 1

Views

Author

Rémy Sigrist, Aug 05 2022

Keywords

Comments

See A071255 for a similar sequence.
The ratio a(n+1)/a(n) tends to Pi^2/6 (A013661) as n tends to infinity.

Examples

			a(1) = 4 and the fourth squarefree number is 5, so a(2) = 5.
		

Crossrefs

Programs

  • C
    See Links section.

Formula

a(n+1) = A005117(a(n)).
Showing 1-4 of 4 results.