A280419 Primes in A132934.
1468910121415161820212224252627283032333435363839, 14689101214151618202122242526272830323334353638394042444546484950515254555657586062636465666869
Offset: 1
Links
- Prime Curios!, 39
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
1 U 4 = 14 and its divisors are 1, 2, 7, 14. Then a(2) = 2. 14 U 6 = 146 and its divisors are 1, 2, 73, 146. Then a(3) = 2. 146 U 8 = 1468 and its divisors are 1, 2, 4, 734, 367, 1468. Then a(4) = 2. 1468 U 9 = 14689 and its divisors are 1, 37, 397, 14689. Then a(5) = 37. Etc.
with(numtheory): T:=proc(t) local x, y; x:=t; y:=0; while x>0 do x:=trunc(x/10); y:=y+1; od; end: P:=proc(q) local a,b,n; b:=1; print(1); for n from 2 to q do if not isprime(n) then b:=n+b*10^T(n); a:=sort([op(divisors(b))]); print(a[2]); fi; od; end: P(10^6); # Paolo P. Lava, Apr 30 2014
Module[{nn=70,cmps},cmps=Select[Range[nn],CompositeQ];Join[ {1},SelectFirst[ Divisors[#],PrimeQ]&/@FromDigits/@Table[ Join[ {1},Flatten[ IntegerDigits/@Take[cmps,n]]],{n,Length[cmps]}]]] (* Harvey P. Dale, Jul 27 2021 *)
Comments