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A286130 Number x = concat(MSD(x),b) such that MSD(x)*b = phi(x), where MSD(x) is the Most Significant Digit of x and phi(x) is the Euler totient function of x. 1
24, 26, 87, 250, 440, 448, 644, 875, 1320, 1640, 1768, 1996, 2480, 2500, 2656, 4400, 6544, 8250, 8360, 8420, 8727, 8875, 13200, 16400, 19984, 19996, 24800, 25000, 25424, 43750, 44000, 45712, 63528, 73840, 75184, 82500, 83346, 83478, 83600, 84200, 132000, 164000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers of the form 25*10^k, 44*10^k, 132*10^k, 164*10^k, 248*10^k, 825*10^k, 836*10^k, 842*10^k, 4375*10^k, 7384*10^k, etc. , with k > 0, are part of the sequence.

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..110

EXAMPLE

phi(63528) = 6*3528 = 21168.

MAPLE

with(numtheory): P:=proc(q) local n; for n from 1 to q do

if phi(n)=trunc(n/10^(ilog10(n)))*(n mod 10^ilog10(n)) then print(n); fi;

od; end: P(10^9);

MATHEMATICA

Select[Range@ 164000, Function[x, First[#] FromDigits[Rest@ #] == EulerPhi@ x &@ IntegerDigits@ x]] (* Michael De Vlieger, May 03 2017 *)

CROSSREFS

Cf. A000010, A000030.

Sequence in context: A053968 A336237 A058627 * A279427 A116203 A345499

Adjacent sequences:  A286127 A286128 A286129 * A286131 A286132 A286133

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, May 03 2017

STATUS

approved

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Last modified January 22 01:28 EST 2022. Contains 350481 sequences. (Running on oeis4.)