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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A117463 Result of the final iteration of doubling in A117462 to equal or exceed n.

Original entry on oeis.org

2, 4, 6, 8, 10, 12, 14, 16, 18, 16, 16, 12, 16, 20, 24, 28, 32, 18, 20, 32, 24, 32, 40, 24, 28, 32, 36, 40, 44, 48, 32, 40, 48, 56, 64, 36, 40, 44, 48, 64, 80, 48, 56, 64, 72, 80, 88, 48, 52, 80, 96, 56, 64, 72, 80, 88, 96, 104, 112, 96, 112, 64, 72, 80, 88, 96, 104, 112, 120, 112, 128
Offset: 0

Views

Author

Enoch Haga, Mar 18 2006

Keywords

Examples

			In a(11) = 16: SOD(11) = 2. 2 doubled is 4,8,16, after A117462(11)= 3 iterations.
		

Crossrefs

Programs

  • Maple
    A117463 := proc(n)
        2^A117462(n)*digsum(n) ;
    end proc:
    seq(A117463(n),n=1..90) ; # R. J. Mathar, Sep 25 2018
  • UBASIC
    10 'use of str,mid,len,val 20 'number of doubled iterations required to equal or exceed sod(n)
    30 C=C+1
    40 D=str(C)
    50 E=len(D)
    60 for Q=2 to E
    70 A=mid(D,Q,1):G=val(A)
    80 I=I+G
    90 next Q
    100 print C;I;"-";
    110 K=I
    120 I=0
    130 for R=1 to C
    140 K=K+K:T=T+1
    150 if K>=C then print C;K;T:cancel for:stop:goto 170
    160 next R
    170 K=0:T=0
    180 goto 30

Formula

a(n) = 2^A117462(n) * A007953(n). - R. J. Mathar, Sep 25 2018

Extensions

Extended by R. J. Mathar, Sep 25 2018

A117458 Primes and their indices such that when their respective SOD's are both prime, the SOD of the index is the nextprime of the prime SOD.

Original entry on oeis.org

227, 313, 1723, 2003, 2311, 2609, 3329, 3701, 4007, 4027, 4801, 4931, 5107, 7253, 10457, 12143, 12163, 12211, 12433, 12547, 13063, 14143, 14341, 14831, 15139, 15373, 16091, 17027, 17047, 19403, 20047, 20261, 21059, 21149, 22157, 23053, 23293, 23431, 24229, 24623
Offset: 1

Views

Author

Enoch Haga, Mar 18 2006

Keywords

Comments

"SOD" = "sum of digits".

Examples

			313 is a term, 65 is the index of the prime 313. The SOD(65) = 11. The SOD(313) = 7. 11 is the next prime after 7.
		

Crossrefs

Programs

  • Mathematica
    Select[Range[25000],  PrimeQ[#] && PrimeQ[Plus @@ IntegerDigits[#]] &&
       NextPrime[Plus @@ IntegerDigits[#]] == Plus @@ IntegerDigits[PrimePi[#]] &] (* Tanya Khovanova, Mar 16 2021 *)

Formula

Individually sum the digits of both prime index and associated prime. If both sums are prime and the sum of the index is the next prime of the prime SOD, add to sequence.

Extensions

Offset changed to 1 by Alois P. Heinz, Mar 16 2021
Showing 1-2 of 2 results.