A024622 -id:A024622 - cp's OEIS frontend

A182908 Rank of 2^n when all prime powers (A246655) p^n, for n>=1, are jointly ranked.

1, 3, 6, 10, 18, 27, 44, 70, 117, 198, 340, 604, 1078, 1961, 3590, 6635, 12370, 23150, 43579, 82267, 155921, 296347, 564688, 1078555, 2064589, 3958999, 7605134, 14632960, 28195586, 54403835, 105102701, 203287169, 393625231, 762951922, 1480223716, 2874422303

Offset: 1

Clark Kimberling, Dec 13 2010

nonn

			a(3)=6 because 2^3 has rank 6 in the sequence (2,3,4,5,7,8,9,...).

Ray Chandler, Table of n, a(n) for n = 1..92 (using b-file file from A007053)

Cf. A000720, A024622, A025528, A246655.

Row 1 of A182869. Complement of A182909.

T[i_,j_]:=Sum[Floor[j*Log[Prime[i]]/Log[Prime[h]]],{h,1,PrimePi[Prime[i]^j]}]; Flatten[Table[T[i,j],{i,1,1},{j,1,22}]]
f[n_] := Sum[ PrimePi[ Floor[2^(n/k)]], {k, n + 1}]; Array[f, 34] (* Robert G. Wilson v, Jul 08 2011 *)

from sympy import primepi, integer_nthroot
def A182908(n):
    x = 1<Chai Wah Wu, Nov 05 2024

a(n) = A182908(n) = A024622(n) - 1 for n>=1.
a(n) = Sum_{i=1..n} pi(floor(2^(n/i))), where pi(n) = A000720(n). - Ridouane Oudra, Oct 26 2020
a(n) = A025528(2^n). - Pontus von Brömssen, Sep 27 2024

Minor edits by Ray Chandler, Aug 20 2021

A376341 Position of first appearance of n in A057820, the sequence of first differences of prime-powers, or 0 if n does not appear.

Original entry on oeis.org

1, 5, 10, 13, 19, 25, 199, 35, 118, 48, 28195587, 61, 3745011205066703, 80, 6635, 312, 1079, 207, 3249254387600868788, 179, 43580, 216, 21151968922, 615, 762951923, 403, 1962, 466, 12371, 245, 1480223716, 783, 494890212533313, 1110, 2064590, 1235, 375744164943287809536

Offset: 1

Gus Wiseman, Sep 22 2024

nonn

For odd n either a(n) or a(n)+1 is in A024622 (unless a(n) = 0), corresponding to cases where the smaller or the larger term in the pair of consecutive prime powers, respectively, is a power of 2. - Pontus von Brömssen, Sep 27 2024

			a(4) = 13, because the first occurrence of 4 in A057820 is at index 13. The corresponding first pair of consecutive prime powers with difference 4 is (19, 23), and a(4) = A025528(23) = 13.
a(61) = A024622(96), because the first pair of consecutive prime powers with difference 61 is (2^96, 2^96+61), and A025528(2^96+61) = A024622(96).

Pontus von Brömssen, Table of n, a(n) for n = 1..60

For compression instead of first appearances we have A376308.
For run-lengths instead of first appearances we have A376309.
For run-sums instead of first appearances we have A376310.
For squarefree numbers instead of prime-powers we have A376311.
The sorted version is A376340.
A000040 lists the prime numbers, differences A001223.
A000961 and A246655 list prime-powers, first differences A057820.
A024619 and A361102 list non-prime-powers, first differences A375708.
A003242 counts compressed compositions, ranks A333489.
A005117 lists squarefree numbers, differences A076259.
A116861 counts partitions by compressed sum, by compressed length A116608.
Cf. A001597, A006549, A007916, A024622, A025475, A025528, A037201, A038664, A053289, A110969, A120430, A174965, A373400, A375706.

mnrm[s_]:=If[Min@@s==1,mnrm[DeleteCases[s-1,0]]+1,0];
q=Differences[Select[Range[100],#==1||PrimePowerQ[#]&]];
Table[Position[q,k][[1,1]],{k,mnrm[q]}]

A057820(a(n)) = n whenever a(n) > 0. - Pontus von Brömssen, Sep 24 2024

Definition modified by Pontus von Brömssen, Sep 26 2024

More terms from Pontus von Brömssen, Sep 27 2024

A089576 Let p_k = k-th prime, let f((p_k)^n) = m where m is the largest power of p_(k+1) < (p_k)^n. a(n) = number of iterations of f to reach 1, starting from n and starting from k = 1.

Original entry on oeis.org

0, 1, 2, 2, 3, 4, 4, 4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 9, 10, 10, 10, 11, 11, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 16, 16, 16, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 20, 20, 20, 21, 21

Offset: 0

Naohiro Nomoto, Dec 29 2003

The steps are a downward recursion in the prime powers: start at 2^n in A000961, i.e., at A000961(A024622(n)); skip to the left to the next smaller power 3^e_3 (see A024623), then to the left to the next smaller power 5^e_5, to the left to the next smaller power 7^e_7 etc., and count the steps to reach 1. - R. J. Mathar, Sep 08 2021

			a(5)=4 as f(2^5)=3^3 < 2^5, f(3^3)=5^2 < 3^3, f(5^2)=7 < 5^2 and f(7)=11^0 < 7.

Michael De Vlieger, Table of n, a(n) for n = 0..10000

Row lengths of A347285.

# largest exponent m of prime(k+1)^m< prime(k)^n.
A089576f := proc(k,n)
    local pkn,pplus,m ;
    pkn := ithprime(k)^n ;
    pplus := ithprime(k+1) ;
    for m from 1 do
        if pplus^m >= pkn then
            return m-1 ;
        end if;
    end do:
end proc:
A089576 := proc(n)
    local itr,m;
    if n = 0 then
        return 0 ;
    end if;
    m := n ;
    for itr from 1 do
        m := A089576f(itr,m) ;
        if m = 0 then
            return itr ;
        end if;
    end do:
end proc:
seq(A089576(n),n=0..80) ; # R. J. Mathar, Sep 07 2021

Array[-1 + Length@ NestWhile[Append[#1, #2^Floor@ Log[#2, #1[[-1]]]] & @@ {#, Prime[Length@ # + 1]} &, {2^#}, #[[-1]] > 1 &] &, 71, 0] (* Michael De Vlieger, Sep 08 2021 *)

More terms from Michael De Vlieger, Sep 08 2021

A192015 Arithmetic derivative of prime powers: a(n) = A003415(A000961(n)).

Original entry on oeis.org

0, 1, 1, 4, 1, 1, 12, 6, 1, 1, 32, 1, 1, 1, 10, 27, 1, 1, 80, 1, 1, 1, 1, 14, 1, 1, 1, 192, 1, 1, 1, 1, 108, 1, 1, 1, 1, 1, 1, 1, 1, 22, 75, 1, 448, 1, 1, 1, 1, 1, 1, 1, 1, 26, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 405, 1, 1024, 1, 1, 1, 1, 1, 1, 1, 34

Offset: 1

Reinhard Zumkeller, Jun 26 2011

nonn

a(A000040(n)) = 1; a(A002808(n)) > 1;
A001787, A027471, A100484, A079705 and A051674 are subsequences;
A001787 and A024622 give record values and where they occur;
A192016(n) = A003415(a(n)).

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Prime Power

a192015 = a003415 . a000961  -- Reinhard Zumkeller, Apr 16 2014

Join[{0}, Reap[For[n = 1, n <= 300, n++, f = FactorInteger[n]; If[Length[f] == 1, Sow[n*Total[Apply[#2/#1&, f, {1}]]]]]][[2, 1]]] (* Jean-François Alcover, Feb 21 2014 *)

from sympy import primepi, integer_nthroot, factorint
def A192015(n):
    if n == 1: return 0
    def f(x): return int(n+x-1-sum(primepi(integer_nthroot(x,k)[0]) for k in range(1,x.bit_length())))
    m, k = n, f(n)
    while m != k:
        m, k = k, f(k)
    return sum((m*e//p for p,e in factorint(m).items())) # Chai Wah Wu, Aug 15 2024

a(n) = A025474(n) * A025473(n)^(A025474(n) - 1).

A192083 Arithmetic derivative of squares of prime powers: a(n) = A003415(A056798(n)).

Original entry on oeis.org

0, 4, 6, 32, 10, 14, 192, 108, 22, 26, 1024, 34, 38, 46, 500, 1458, 58, 62, 5120, 74, 82, 86, 94, 1372, 106, 118, 122, 24576, 134, 142, 146, 158, 17496, 166, 178, 194, 202, 206, 214, 218, 226, 5324, 18750, 254, 114688, 262, 274, 278, 298, 302, 314, 326, 334

Offset: 1

Reinhard Zumkeller, Jun 26 2011

nonn

A001787 and A024622 give record values and where they occur.

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A003415, A024622, A025473, A025474, A056798, A192084.

Subsequences: A001787, A027471, A051674, A079705, A100484.

s[n_] := If[PrimePowerQ[n], f = FactorInteger[n][[1]]; 2*f[[2]]*n^(2 - 1/f[[2]]), Nothing]; s[1] = 0; Array[s, 200] (* Amiram Eldar, Apr 06 2025 *)

a(n) = 2 * A025474(n) * A025473(n)^(2*A025474(n) - 1).

A192084(n) = A003415(a(n)).

cp's OEIS Frontend

A182908 Rank of 2^n when all prime powers (A246655) p^n, for n>=1, are jointly ranked.

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A376341 Position of first appearance of n in A057820, the sequence of first differences of prime-powers, or 0 if n does not appear.

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A089576 Let p_k = k-th prime, let f((p_k)^n) = m where m is the largest power of p_(k+1) < (p_k)^n. a(n) = number of iterations of f to reach 1, starting from n and starting from k = 1.

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A192015 Arithmetic derivative of prime powers: a(n) = A003415(A000961(n)).

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A192083 Arithmetic derivative of squares of prime powers: a(n) = A003415(A056798(n)).

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Programs

Mathematica

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