A272778 Numbers n such that sigma(n) = concat(s,t) and n = s * t, where sigma(n) is the sum of the divisors of n.

48, 1040, 1196, 2720, 6080, 19080, 116644, 252800, 796172, 1014800, 2370352, 2796800, 2864000, 12200288, 13499120, 13716716, 15252992, 21938672, 33883520, 43218800, 62496048, 70240000, 98392832, 129704960, 199361792, 318836720, 548444160, 1218624080

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..46 (terms < 2.5*10^11)

Example

sigma(48) = 124 = concat(12,4) and 12 * 4 = 48;
sigma(1196) = 2352 = concat(23,52) = and 23 * 52 = 1196.

Maple

with(numtheory): P:=proc(q) local a, b, c, i, n;
for n from 1 to q do c:=sigma(n); for i from 1 to ilog10(c) do
a:=trunc(c/10^i);  b:=c-a*10^i; if a*b=n then print(n); break;
fi; od; od; end: P(10^9);

Mathematica

Select[Range[3*10^5], Function[n, Total@ Boole@ Function[k, n == First@ # Last@ # & /@ Map[FromDigits /@ TakeDrop[IntegerDigits@ k, #] &, Range[IntegerLength@ k - 1]]][DivisorSigma[1, n]] > 0]] (* Michael De Vlieger, May 07 2016, Version 10.2 *)

Crossrefs

Cf. A000203, A272779.

Sequence in context: A274806 A292045 A341306 * A160068 A229387 A010839

Adjacent sequences: A272775 A272776 A272777 * A272779 A272780 A272781

Keyword

nonn,base

Author

Paolo P. Lava, May 06 2016

Extensions

a(11)-a(28) from Giovanni Resta, May 06 2016

Status

approved