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A232093 Position of 7^n among 7-smooth numbers (A002473). 1
1, 7, 30, 87, 202, 403, 726, 1214, 1911, 2874, 4158, 5832, 7968, 10640, 13933, 17937, 22747, 28464, 35195, 43054, 52162, 62644, 74630, 88257, 103671, 121020, 140462, 162155, 186267, 212973, 242453, 274894, 310483, 349420, 391909, 438161, 488388, 542814, 601667, 665181, 733594, 807154, 886109, 970720, 1061252, 1157972, 1261156, 1371084, 1488047, 1612341 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Note that all powers of 7 are terms in A002473.

Polynomial of fourth order is sufficient for very accurate approximation of a(n).

LINKS

Zak Seidov, Table of n, a(n) for n = 0..200

EXAMPLE

A002473(a(1)) = A002473(7) = 7,

A002473(a(2)) = A002473(30) = 49 = 7^2,

A002473(a(200)) = A002473(411921660) = 7^200.

MATHEMATICA

ss7 = {}; Do[m = 7^n; s = Sum[1 + Floor[Log[2, 7^(n - k)/5^i/3^j]], {k, 0, n}, {i, 0, Log[5, 7^(n - k)]}, {j, 0, Log[3, 7^(n - k)/5^i]}]; AppendTo[ss2, {n, s}], {n, 0, 50}]

CROSSREFS

Cf. A002473, A232067.

Sequence in context: A083474 A030440 A256225 * A045889 A038739 A038798

Adjacent sequences:  A232090 A232091 A232092 * A232094 A232095 A232096

KEYWORD

nonn

AUTHOR

Zak Seidov, Nov 18 2013

STATUS

approved

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Last modified March 23 12:43 EDT 2019. Contains 321430 sequences. (Running on oeis4.)