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
Examples
a(5) = 51 because 51 = 3 * 17 is a semiprime that starts with 5, and is the least such semiprime.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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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]);