A216391 Number of values of k for which phi(k) is a permutation of decimal digits of k, for k < 2^n.

1, 1, 1, 1, 2, 3, 3, 3, 5, 5, 5, 8, 19, 21, 34, 55, 81, 130, 221, 407, 515, 850, 1787, 2287, 3968, 8176, 12332

Offset

1,5

Comments

Partial sums of A216394.

Links

Table of n, a(n) for n=1..27.

Formula

a(n) = # { k in A115921 | k < 2^n }. - M. F. Hasler, Feb 24 2014

Example

a(12) = 8 because the values of k satisfying the condition for k < 2^12 are {1, 21, 63, 291, 502, 2518, 2817, 2991}. - V. Raman, Feb 18 2014

Maple

A216391 := proc(n)
    local a, k, kdgs, pdgs ;
    a := 0 ;
    for k from 1 to 2^n do
        kdgs := sort(convert(k, base, 10)) ;
        numtheory[phi](k) ;
        pdgs := sort(convert(%, base, 10)) ;
        if pdgs = kdgs then
            a := a+1 ;
        end if;
    end do:
    a ;
end proc:
for n from 1 do
    print(A216391(n)) ;
end do: # R. J. Mathar, Mar 04 2014

Prog

(PARI) a(n)=sum(k=1, 2^n, vecsort(digits(k)) == vecsort(digits(eulerphi(k)))) \\ V. Raman, Feb 18 2014, edited by M. F. Hasler, Mar 04 2014

Crossrefs

Cf. A115921, A000010.

Sequence in context: A234968 A141784 A234337 * A014202 A309247 A238211

Adjacent sequences: A216388 A216389 A216390 * A216392 A216393 A216394

Keyword

nonn,base,more

Author

V. Raman, Sep 06 2012

Status

approved