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A239245
Let y be the sum of the numbers x not coprime to n, with x<=n. Sequence lists n such that digits of y end in "n". Primes are excluded.
1
240, 5625, 40625, 1640625, 4140625, 39495680, 47265625, 56640625, 3574214656, 66247700480, 115760971776
OFFSET
1,1
COMMENTS
n/2*(n+1-phi(n)) is of the form 'm' U 'n'.
Primes are banal solutions. In fact if p is prime we have that phi(p) = p-1 and p/2*(p+1-(p-1)) = p/2*(2) = p.
EXAMPLE
phi(240) = 64; 240/2*(241-64) = 21240 that is "212" U "240".
MAPLE
with(numtheory); P:=proc(q) local a, b, n;
for n from 1 to q do a:=n; b:=0; while a>0 do b:=b+1; a:=trunc(a/10); od;
if n=(((n/2*(n+1-phi(n))) mod 10^b) then print(n); fi; od; end: P(10^9);
CROSSREFS
Sequence in context: A249533 A324070 A145094 * A218131 A268637 A264317
KEYWORD
nonn,more,base
AUTHOR
Paolo P. Lava, Mar 13 2014
EXTENSIONS
a(6)-a(11) from Giovanni Resta, Mar 14 2014
STATUS
approved