OFFSET
1,1
COMMENTS
All prime numbers p > 5 must be multiplied by 1+10^k, where k is the number of digits of p. The result is p U p. - Paolo P. Lava, Apr 11 2008
REFERENCES
Giorgio Balzarotti and Paolo P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 100.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(8) = 6 because 8*6 = 48 and 6 is the minimum number that multiplied by 8 gives a number ending in 8.
a(12) = 26 because 12*26 = 312 and 26 is the minimum number that multiplied by 12 gives a number ending in 12.
MAPLE
P:=proc(n) local a, b, i, j; print(11); for i from 2 by 1 to n do b:=trunc(evalf(log10(i)))+1; for j from 2 by 1 to n do a:=i*j; if i=a-trunc(a/10^b)*10^b then print(j); break; fi; od; od; end: P(101); # Paolo P. Lava, Apr 11 2008
MATHEMATICA
snrd[n_]:=Module[{k=2}, While[Mod[k*n, 10^IntegerLength[n]]!=n, k++]; k]; Array[ snrd, 70] (* Harvey P. Dale, Apr 08 2019 *)
PROG
(Python)
def a(n):
kn, s = 2*n, str(n)
while not str(kn).endswith(s): kn += n
return kn//n
print([a(n) for n in range(1, 66)]) # Michael S. Branicky, Nov 06 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, Oct 18 2006
STATUS
approved