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.

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A107826 Indices of primes occurring in A107806.

Original entry on oeis.org

6, 2, 9, 1, 10, 8, 5, 7, 4, 12, 11, 13, 14, 15, 19, 18, 20, 21, 16, 3, 17, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107826(n)=pi(A107806(n))

A107827 Indices of primes occurring in A107807.

Original entry on oeis.org

7, 4, 12, 2, 6, 5, 8, 10, 1, 9, 11, 13, 14, 15, 19, 18, 20, 21, 16, 3, 17, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107827(n)=pi(A107807(n))

A107828 Indices of primes occurring in A107808.

Original entry on oeis.org

8, 5, 6, 2, 9, 1, 10, 17, 3, 16, 11, 7, 4, 12, 14, 13, 15, 19, 18, 20, 21, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107828(n)=pi(A107808(n))

A107829 Indices of primes occurring in A107809.

Original entry on oeis.org

9, 1, 10, 8, 5, 6, 2, 11, 7, 4, 12, 14, 13, 15, 19, 18, 20, 21, 16, 3, 17, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107829(n) = pi(A107809(n)).

A107830 Indices of primes occurring in A107810.

Original entry on oeis.org

10, 1, 9, 2, 6, 5, 7, 4, 12, 11, 8, 13, 14, 15, 19, 18, 20, 21, 16, 3, 17, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107830(n)=pi(A107810(n))

A107831 Indices of primes occurring in A107811.

Original entry on oeis.org

11, 2, 6, 5, 7, 4, 12, 9, 1, 10, 8, 13, 14, 15, 19, 18, 20, 21, 16, 3, 17, 22, 24, 23, 27, 26, 28, 25, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107831(n)=pi(A107811(n))

A107832 Indices of primes occurring in A107812.

Original entry on oeis.org

12, 2, 6, 5, 7, 4, 15, 13, 8, 10, 1, 9, 11, 14, 16, 3, 17, 22, 19, 18, 20, 21, 23, 24, 25, 28, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61
Offset: 1

Views

Author

Zak Seidov, May 24 2005

Keywords

Crossrefs

Formula

A107832(n)=pi(A107812(n))

A381130 a(n) is the smallest prime not yet in the sequence that contains a substring of size 2 from a(n-1); a(1)=11.

Original entry on oeis.org

11, 113, 13, 131, 31, 311, 211, 421, 521, 523, 23, 223, 227, 127, 271, 71, 571, 157, 151, 251, 257, 457, 557, 577, 277, 677, 67, 167, 163, 263, 269, 569, 563, 463, 461, 61, 613, 137, 37, 337, 233, 239, 139, 313, 317, 17, 173, 73, 373, 379, 79, 179, 479, 47
Offset: 1

Views

Author

Enrique Navarrete, Feb 14 2025

Keywords

Crossrefs

Programs

  • Python
    from itertools import count, islice
    from sympy import isprime, nextprime
    def agen(): # generator of terms
        aset, an, minp = set(), 11, 13
        while True:
            yield an
            aset.add(an)
            s = str(an)
            targets = set(s[i:i+2] for i in range(len(s)-1))
            p = minp
            w = str(p)
            while p in aset or not any(t in w for t in targets):
                p = nextprime(p)
                w = str(p)
            while minp in aset:
                minp = nextprime(minp)
            an = p
    print(list(islice(agen(), 54))) # Michael S. Branicky, Apr 15 2025

A284146 a(n+1) is the smallest prime not already in the sequence which shares no digit with a(n).

Original entry on oeis.org

2, 3, 5, 7, 11, 23, 17, 29, 13, 47, 19, 37, 41, 53, 61, 43, 59, 31, 67, 83, 71, 89, 73, 101, 79, 103, 97, 113, 227, 109, 223, 107, 229, 131, 257, 139, 277, 149, 233, 151, 239, 157, 263, 179, 283, 167, 293, 181, 269, 137, 409, 127, 349
Offset: 1

Views

Author

Zak Seidov, Mar 20 2017

Keywords

Comments

The sequence is not a permutation of prime numbers.
E.g., after calculating 2001 terms of the sequence, the first absent primes are 1973,3719,3917,7193,9137,9173,9371. It's evident that these numbers will never appear in the sequence because any last term of the sequence should use at least one of digits 1,3,7,9.
The first nine terms {2, 3, 5, 7, 11, 23, 17, 29, 13} coincide with A068863(1..9).
The only fixed points are a(n) for n={1, 2, 3, 4, 5, 7, 12, 13, 17, 19} are {2, 3, 5, 7, 11, 17, 37, 41, 59, 67} that is for these n's a(n)=prime(n)=A000040(n).
a (100*k) for k = 1,20: {443, 1193, 1741, 1621, 4567, 6047, 5851, 6491, 7151, 7559, 9349, 10601, 11119, 11699, 13001, 11839, 14107, 16111, 15073, 16487}.

Crossrefs

Programs

  • Mathematica
    a = {2}; While[ Length[a] < 100, d = IntegerDigits@ Last@ a; p = 2; While[ Intersection[ IntegerDigits@p, d] != {} || MemberQ[a, p], p = NextPrime@ p]; AppendTo[a, p]]; a (* Giovanni Resta, Mar 21 2017 *)

A379140 Numbers k such that the greatest prime < 10^k and the least prime > 10^k share no decimal digits.

Original entry on oeis.org

1, 2, 8, 11, 15, 16, 17, 18, 21, 25, 26, 30, 40, 44, 46, 47, 50, 51, 53, 55, 60, 63, 64, 74, 77, 81, 86, 88, 89, 93, 95, 101, 123, 130, 131, 133, 134, 140, 152, 154, 158, 161, 164, 166, 176, 181, 189, 192, 198, 209, 214, 215, 233, 245, 264, 268, 274, 291, 293, 295, 297, 324, 326, 334, 352, 357
Offset: 1

Views

Author

Robert Israel, Dec 16 2024

Keywords

Comments

Charles R Greathouse IV conjectures that A107801(n) = prime(n) for n sufficiently large (and similarly for other related sequences). If that is the case, this sequence must be finite.

Examples

			a(3) = 8 is a term because the greatest prime < 10^8 and the least prime > 10^8 are 99999989 and 100000007 respectively, and these have no digits in common.
5 is not a term because the greatest prime < 10^5 and the least prime > 10^5 are 99991 and 100003 respectively, and these have digit 1 in common.
		

Crossrefs

Programs

  • Maple
    filter:= t -> convert(convert(prevprime(10^t),base,10),set) intersect convert(convert(nextprime(10^t),base,10),set) = {}:
    select(filter, [$1..400]);
Previous Showing 21-30 of 31 results. Next