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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

David W. Wilson

STATUS

approved

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