login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A225756 Runs of consecutive numbers with the same number of divisors. 3
2, 3, 14, 15, 21, 22, 26, 27, 33, 34, 35, 38, 39, 44, 45, 57, 58, 75, 76, 85, 86, 87, 93, 94, 95, 98, 99, 104, 105, 116, 117, 118, 119, 122, 123, 133, 134, 135, 136, 141, 142, 143, 145, 146, 147, 148, 158, 159, 171, 172, 177, 178, 189, 190, 201, 202, 203 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first run of length 3 is {33,34,35}; the first of length 4: {116, 117, 118, 119}; of length 5: {2641, 2642, 2643, 2644, 2645}; of length 6: {1081, 1082, 1083, 1084, 1085, 1086}; of length 7: {25781, 25782, 25783, 25784, 25785, 25786, 25787}; of length 8: {77673, 77674, 77675, 77676, 77677, 77678, 77679, 77680}.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

EXAMPLE

Sequence begins:

2, 3;

14, 15;

21, 22;

26, 27;

33, 34, 35;

38, 39;

etc.

MATHEMATICA

sel = Select[Range[300], DivisorSigma[0, #] == DivisorSigma[0, # + 1] &]; Union[sel, sel + 1]

Flatten[SequencePosition[DivisorSigma[0, Range[300]], {x_, x_}]]//Union (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 22 2021 *)

CROSSREFS

Cf. A225757 (same sum of divisors).

Cf. A225758 (same number and sum of divisors).

Cf. A140578 (first term of every run).

Sequence in context: A056435 A244295 A032806 * A260143 A275303 A281500

Adjacent sequences:  A225753 A225754 A225755 * A225757 A225758 A225759

KEYWORD

nonn,easy,tabf

AUTHOR

Jean-François Alcover, May 15 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 20 01:18 EST 2022. Contains 350467 sequences. (Running on oeis4.)