login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A044072 Numbers k such that string 2,3 occurs in the base 4 representation of k but not of k-1. 3
11, 27, 43, 59, 75, 91, 107, 123, 139, 155, 171, 203, 219, 235, 251, 267, 283, 299, 315, 331, 347, 363, 379, 395, 411, 427, 459, 475, 491, 507, 523, 539, 555, 571, 587, 603, 619, 635, 651, 667, 683, 779, 795, 811, 827, 843, 859, 875, 891, 907, 923, 939, 971 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Members are of form 16k+11, but not all such numbers are in the sequence. The first missing number is 187.

LINKS

Michael S. Branicky, Table of n, a(n) for n = 1..10000

MATHEMATICA

Flatten[Position[Partition[Table[If[MemberQ[Partition[IntegerDigits[n, 4], 2, 1], {2, 3}], 1, 0], {n, 1000}], 2, 1], {0, 1}]] + 1 (* Vincenzo Librandi, Aug 19 2015 *)

PROG

(Python)

from sympy.ntheory.factor_ import digits

def has23(n): return "23" in "".join(map(str, digits(n, 4)[1:]))

def ok(n): return has23(n) and not has23(n-1)

print([k for k in range(972) if ok(k)]) # Michael S. Branicky, Nov 27 2021

CROSSREFS

Differs from A106839.

Cf. A044453.

Sequence in context: A152574 A035701 A106839 * A044453 A212776 A137019

Adjacent sequences:  A044069 A044070 A044071 * A044073 A044074 A044075

KEYWORD

nonn,base,changed

AUTHOR

Clark Kimberling

EXTENSIONS

a(48) and beyond from Michael S. Branicky, Nov 27 2021

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 December 5 15:06 EST 2021. Contains 349557 sequences. (Running on oeis4.)