A085981 Number of 7's in decimal expansion of prime(n).

0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 2, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1

Offset: 1

Author

Jason Earls, Jul 06 2003

Keywords

• base
• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. 0's A085974, 1's A085975, 2's A085976, 3's A085977, 4's A085978, 5's A085979, 6's A085980, 8's A085982, 9's A085983.

Programs

Haskell

a085981 = count7 0 . a000040 where
   count7 c x | d == 7    = if x < 10 then c + 1 else count7 (c + 1) x'
              | otherwise = if x < 10 then c else count7 c x'
              where (x', d) = divMod x 10
-- Reinhard Zumkeller, Apr 08 2014

Mathematica

DigitCount[Prime[Range[100]],10,7] (* Paolo Xausa, Oct 30 2023 *)