OFFSET
0,1
LINKS
Paolo P. Lava and Giovanni Resta, Table of n, a(n) for n = 0..10000 (first 500 terms from Paolo P. Lava)
EXAMPLE
The sum of the products of pairs of consecutive digits of 25 is 2*5 = 10 and 25 is the least number with this property, so a(10) = 25.
The sum of the products of pairs of consecutive digits of 219 is 2*1 + 1*9 = 11. Again, 219 is the least number with this property, so a(11) = 219.
MAPLE
P:=proc(q) local a, b, c, k, j, n; print(10);
for j from 1 to q do for n from 1 to q do a:=n; b:=[];
for k from 1 to ilog10(n)+1 do b:=[(a mod 10), op(b)];
a:=trunc(a/10); od; a:=add(b[k]*b[k+1], k=1..nops(b)-1);
if a=j then print(n); break; fi; od; od; end: P(10^6);
MATHEMATICA
Join[{10}, With[{tbl=Table[{n, Total[Times@@@Partition[ IntegerDigits[ n], 2, 1]]}, {n, 1400}]}, Flatten[Table[Select[tbl, #[[2]]==k&, 1], {k, 60}], 1]][[All, 1]]] (* Harvey P. Dale, Jun 15 2017 *)
PROG
(PARI) a(n)=k=10; while(sum(i=1, #digits(k)-1, digits(k)[i]*digits(k)[i+1])!=n, k++); k
vector(50, n, n--; a(n)) \\ Derek Orr, May 19 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, May 14 2015
STATUS
approved