OFFSET
1,1
COMMENTS
This sequence contains all squarefree numbers of A308099.
EXAMPLE
1426 is such a number because it is a squarefree composite, with prime factors in ascending order 2, 23 and 31 which are chained.
MATHEMATICA
Select[Range@1500, SquareFreeQ@#&&PrimeNu@#>1&&And@@(Last@#[[1]]==First@#[[2]]&/@Partition[IntegerDigits@*First/@FactorInteger@#, 2, 1])&]
PROG
(PARI) isok(n) = {my(f=factor(n)[, 1]); if ((#f <= 1) || !issquarefree(n), return(0)); my(vd=digits(f[1]), d=vd[#vd], vd2, d2); if ((#f <= 1) || !issquarefree(n), return(0)); for (k=2, #f, vd2 = digits(f[k]); d2 = vd2[1]; if (d2 != d, return (0)); vd = vd2; d = vd[#vd]; ); return (1); } \\ Michel Marcus, May 18 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Giorgos Kalogeropoulos, May 17 2019
STATUS
approved