A374899 a(n) is the least semiprime that starts with n.

10, 21, 33, 4, 51, 6, 74, 82, 9, 10, 111, 121, 133, 14, 15, 161, 177, 183, 194, 201, 21, 22, 235, 247, 25, 26, 274, 287, 291, 301, 314, 321, 33, 34, 35, 361, 371, 38, 39, 403, 411, 422, 437, 445, 451, 46, 471, 481, 49, 501, 51, 526, 533, 542, 55, 562, 57, 58, 591, 6001, 611, 62, 633, 649, 65, 662

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(5) = 51 because 51 = 3 * 17 is a semiprime that starts with 5, and is the least such semiprime.

Maple

f:= proc(n) local d, x;
  if numtheory:-bigomega(n)=2 then return n fi;
  for d from 1 do
    for x from n*10^d to (n+1)*10^d-1 do
      if numtheory:-bigomega(x)=2 then return x fi
  od od
end proc:
map(f, [$1..100]);

Crossrefs

Cf. A001358, A018800, A374897.

Sequence in context: A017509 A184989 A072806 * A189402 A051942 A250664

Adjacent sequences: A374896 A374897 A374898 * A374900 A374901 A374902

Keyword

nonn,base,look

Author

Robert Israel, Jul 22 2024

Status

approved