



3, 21, 147, 1029, 7203, 50421, 352947, 2470629, 17294403, 121060821, 847425747, 5931980229, 41523861603, 290667031221, 2034669218547, 14242684529829, 99698791708803, 697891541961621, 4885240793731347, 34196685556119429
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OFFSET

0,1


COMMENTS

Essentially first differences of A120741.
Second binomial transform of A005053 without initial term 1.
Inverse binomial transform of A103333 without initial term 1.
Second inverse binomial transform of A013708.
Except for first term 3, these are the integers that satisfy phi(n) = 4*n/7.  Michel Marcus, Jul 14 2015
Number of distinct quadratic residues (QR) over Z_7^n such that gcd(QR, 7^n) = 1 where n >= 1.  Param Mayurkumar Parekh, Feb 11 2023


LINKS



FORMULA

a(n) = 7*a(n1) for n > 0; a(0) = 3.
G.f.: 3/(17*x).


PROG

(Magma) [ 3*7^n: n in [0..19] ];


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



