A281592
Products of three distinct primes p1, p2 and p3 (sphenic numbers) with p1
138, 777, 4642, 10258, 10263, 12207, 13282, 16167, 19762, 30783, 37407, 38482, 46978, 48927, 56127, 60145, 63543, 73767, 81687, 89823, 95367, 95627, 103863, 110905, 115527, 128545, 202705, 208879, 223643, 284119, 324947, 325793, 360151, 395003, 477538, 541163, 558322, 585538, 672199, 673693, 780082, 914551, 1016643
Offset: 1
Examples
10258 is in the sequence because 10258 = 2*23*223 and 223 is the concatenation of 2 with 23.
Programs
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Mathematica
c[x_, y_] := x 10^IntegerLength[y] + y; upto[mx_] := Sort@ Reap[Block[{p=2, q=3, v=1}, While[v <= mx, While[p < q && (v = p q (r = c[p, q])) <= mx, If[PrimeQ@r, Sow@v]; p = NextPrime[p]]; p=2; q = NextPrime[q]; v = p q c[p, q]]]][[2, 1]]; upto[10^6] (* Giovanni Resta, Apr 14 2017 *) -
PARI
isok(n) = f = factor(n); ((#f~ == 3) && (vecmax(f[,2]) == 1) && (f[3,1] == fromdigits(concat(digits(f[1,1]), digits(f[2,1]))))); \\ Michel Marcus, Apr 14 2017