The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A020465 Primes that contain digits 4 and 7 only. 5
 7, 47, 4447, 7477, 44777, 47777, 74747, 77447, 77477, 77747, 4444747, 4447747, 4747747, 4774477, 4774747, 7444477, 7447777, 7474477, 7477777, 7747477, 7774777, 7777447, 44447747, 44747447, 44747777, 44774777, 47447747, 47774477, 47774747 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..20000 (first 1000 terms from Vincenzo Librandi) James Maynard and Brady Haran, Primes without a 7, Numberphile video (2019) MATHEMATICA Flatten[Table[Select[FromDigits/@Tuples[{4, 7}, n], PrimeQ], {n, 8}]] (* Vincenzo Librandi, Jul 27 2012 *) PROG (MAGMA) [p: p in PrimesUpTo(47774747) | Set(Intseq(p)) subset [4, 7]]; // Vincenzo Librandi, Jul 27 2012 CROSSREFS Sequence in context: A013399 A013403 A013401 * A092480 A292067 A088143 Adjacent sequences:  A020462 A020463 A020464 * A020466 A020467 A020468 KEYWORD nonn,base AUTHOR STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 30 20:55 EST 2020. Contains 338812 sequences. (Running on oeis4.)