A279058 Least number k = concat(x,y) such that k = n*(x+y) - x * y , -1 if such a number does not exist.

17, 13, 25, 11, 33, 55, 41, 10, 126, 224, 189, 268, 434, 106, 729, 1539, 981, 315, 1079, 313, 844, 416, 415, 1178551, 1373, 309, 1471, 1575, 721, 1456, 1667, 1133, 820, 306, 818, 612, 1961, 305, 2059, 1224, 406, 1530, 2255, 1527, 2353, 2142, 1217, 1420, 101, 303

Offset

3,1

Comments

a(10^k) = 10^k, for k>=1.

MSD of y can be 0.

In the first 1000 terms only 30060 is present two times, in a(354) and a(480).

Links

Paolo P. Lava, Table of n, a(n) for n = 3..1000

Example

a(11) = 126 = concat(12,6) and 11*(12 + 6) - 12*6 = 126;
a(222) =  3921381 = concat(39,21381) and 222*(39 + 21381) - 39*21381 = 3921381.

Maple

with(numtheory): P:=proc(q) local j, k, s, t, n, ok;
for j from 3 to q do ok:=1; for n from 1 to q do if ok=0 then break; else
for k from 1 to ilog10(n) do s:=n mod 10^k; t:=trunc(n/10^k);
if j*(s+t)-s*t=n then print(n); ok:=0; break; fi; od; fi; od; od; end: P(10^6);

Crossrefs

Cf. A278935.

Sequence in context: A063518 A168250 A089502 * A357190 A195534 A128158

Adjacent sequences: A279055 A279056 A279057 * A279059 A279060 A279061

Keyword

nonn,base

Author

Paolo P. Lava, Dec 05 2016

Extensions

a(258) by Giovanni Resta, Dec 05 2016

Status

approved