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 1-5 of 5 results.

A116125 Numbers k such that k concatenated with k-5 gives the product of two numbers which differ by 6.

Original entry on oeis.org

7, 97, 205, 300, 477, 732, 997, 1920, 3157, 9997, 52896, 99997, 120085, 427020, 999997, 8264460, 9999997, 88581312, 99999997, 112000885, 112917765, 143075580, 152863360, 193537077, 233788192, 266755221, 313680096
Offset: 1

Views

Author

Giovanni Resta, Feb 06 2006

Keywords

Comments

Also numbers k such that k concatenated with itself gives the product of two numbers which differ by 4.

Examples

			6786111717//6786111712 = 8237785936 * 8237785942, where // denotes concatenation.
		

Crossrefs

Extensions

Edited by N. J. A. Sloane, Apr 15 2007

A116275 Numbers k such that k*(k+4) gives the concatenation of two numbers m and m-2.

Original entry on oeis.org

8872, 9009, 83352840, 99000099, 329767122286, 670232877711, 738226276371, 933006600339, 999000000999, 3779410975143113, 3872816717528065, 4250291784692548, 4278630943941865, 4372036686326817, 4749511753491300, 5250488246508697, 5627963313673180, 5721369056058132
Offset: 1

Views

Author

Giovanni Resta, Feb 06 2006

Keywords

Examples

			99000099 * 99000103 = 98010199//98010197, where // denotes concatenation.
		

Crossrefs

Programs

  • Python
    from itertools import count, islice
    from sympy import sqrt_mod
    def A116275_gen(): # generator of terms
        for j in count(0):
            b = 10**j
            a = b*10+1
            for k in sorted(sqrt_mod(2,a,all_roots=True)):
                if a*(b+3) <= k**2-2 < a*(a+2):
                    yield k-2
    A116275_list = list(islice(A116275_gen(),30)) # Chai Wah Wu, Feb 19 2024

Extensions

a(16)-a(18) from Chai Wah Wu, Feb 19 2024

A116287 Numbers k such that k*(k+3) gives the concatenation of a number m with itself.

Original entry on oeis.org

8, 98, 767, 858, 910, 998, 3285, 6713, 9998, 45452, 54546, 99998, 990100, 999998, 8181819, 9999998, 70588233, 99999998, 343130554, 362637363, 363636361, 420053631, 421052632, 497975709, 502024289, 578947366, 579946367, 636363637, 637362635, 656869444, 706766918, 713286714, 714285712, 783689995
Offset: 1

Views

Author

Giovanni Resta, Feb 06 2006

Keywords

Comments

From Robert Israel, Apr 08 2025: (Start)
Numbers k such that k * (k + 3) = (10^d + 1) * m for some d and m where m has d digits.
Contains 10^d-2 for all d >= 1. (End)

Crossrefs

Programs

  • Maple
    q:= proc(d,m) local R,t,a,b,x,q;
       t:= 10^d+1;
       R:= NULL;
       for a in numtheory:-divisors(t) do
         b:= t/a;
         if igcd(a,b) > 1 then next fi;
         for x from chrem([0,-m],[a,b]) by t do
           q:= x*(x+m)/t;
           if q >= 10^d then break fi;
           if q >= 10^(d-1) then R:= R, x fi;
       od od;
       sort(convert({R},list));
    end proc:
    seq(op(q(d,3)),d=1..10); # Robert Israel, Apr 08 2025

Extensions

More terms from Robert Israel, Apr 08 2025

A116289 Numbers k such that k*(k+5) gives the concatenation of a number m with itself.

Original entry on oeis.org

6, 96, 385, 429, 567, 611, 814, 996, 4521, 5475, 9996, 90910, 99996, 316832, 683164, 999996, 3636364, 6363632, 9999996, 82352942, 99999996, 331668332, 368421053, 395604391, 442767754, 461538462, 488721800, 511278196, 538461534, 557232242, 604395605, 631578943, 668331664, 700089385, 727272728
Offset: 1

Views

Author

Giovanni Resta, Feb 06 2006

Keywords

Comments

From Robert Israel, Apr 09 2025: (Start)
Numbers k such that k * (k + 5) = (10^d + 1) * m for some d and m where m has d digits.
Contains 10^d-4 for all d >= 1. (End)

Crossrefs

Programs

  • Maple
    q:= proc(d,m) local R,t,a,b,x,q;
       t:= 10^d+1;
       R:= NULL;
       for a in numtheory:-divisors(t) do
         b:= t/a;
         if igcd(a,b) > 1 then next fi;
         for x from chrem([0,-m],[a,b]) by t do
           q:= x*(x+m)/t;
           if q >= 10^d then break fi;
           if q >= 10^(d-1) then R:= R, x fi;
       od od;
       sort(convert({R},list));
    end proc:
    seq(op(q(d,5)),d=1..10); # Robert Israel, Apr 09 2025

Extensions

More terms from Robert Israel, Apr 09 2025

A116297 Numbers k such that k*(k+4) gives the concatenation of two numbers m and m+1.

Original entry on oeis.org

2, 5, 43, 54, 38161, 61836, 83616, 346978, 653019, 950049, 8647553, 9534263, 8167822281, 9007920990, 9209900790, 9950000499, 4737445289219, 4990568257185, 5009431742812, 5262554710778, 8373808925583
Offset: 1

Views

Author

Giovanni Resta, Feb 06 2006

Keywords

Crossrefs

Showing 1-5 of 5 results.