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A240897
Consider a number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that phi(n) = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(j)*10^(j-1)})} (see example below).
2
26, 36, 370, 570, 3270, 11746, 21630, 24490, 24806, 56980, 117404, 468430, 595270, 1228070, 3390486, 4784660, 7898490, 9773610, 10529610, 10993626, 12835226, 13094276, 27797386, 30987000, 64644060, 216393030, 291661606, 660619830, 990261270, 1217516566
OFFSET
1,1
EXAMPLE
If n = 11746, starting from the least significant digit, let us cut the number into the set 6, 46, 746, 1746. We have:
sigma(6) = 12;
sigma(46) = 72;
sigma(746) = 1122;
sigma(1746) = 3822
and 12 + 72 + 1122 + 3822 = 5028 = phi(11746).
MAPLE
with(numtheory); P:=proc(q) local a, k, n;
for n from 2 to q do a:=0; k:=1; while (n mod 10^k)<n do
a:=a+sigma(n mod 10^k); k:=k+1; od;
if phi(n)=a then print(n); fi; od; end: P(10^9);
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Apr 14 2014
EXTENSIONS
a(14)-a(30) from Giovanni Resta, Apr 16 2014
STATUS
approved