OFFSET
1,1
REFERENCES
P. Vaderlind, R. K. Guy and L. C. Larsen, The Inquisitive Problem Solver, Math. Assoc. Am., 2002, Problem P185.
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..10000
EXAMPLE
12*21 = 252 = 12*21, 403 = 13*31, 574 = 14*41, etc
PROG
(PARI) {for(n=100, 15000, k=floor(log(n)/log(100)); f=divisors(n); v=[]; for(h=1, matsize(f)[2], if(10^k<f[h]&&f[h]<10^(k+1), v=concat(v, f[h]))); b=matsize(v)[2]; if(b>1, w=[]; for(i=1, b, s=[]; a=v[i]; while(a>0, d=divrem(a, 10); a=d[1]; s=concat(d[2], s)); w=concat(w, [vecsort(s)])); c=0; for(i=1, b-1, for(j=i+1, b, if(c<1&&w[i]==w[j], if(v[i]*v[j]==n, print1(n, ", "); c=1))))))}
(Python)
from math import isqrt
from sympy import divisors
def ok(n): return isqrt(n)**2<n and any(sorted(str(d)) == sorted(str(n//d)) for d in divisors(n)[1:-1])
print([k for k in range(16100) if ok(k)]) # Michael S. Branicky, Sep 08 2024
CROSSREFS
KEYWORD
base,nonn
AUTHOR
N. J. A. Sloane, Nov 11 2002
EXTENSIONS
Extended by Klaus Brockhaus, Nov 12 2002
a(42) and beyond from Michael S. Branicky, Sep 08 2024
STATUS
approved