A037047 Starting at n, "say what you see"; sequence gives number of primes obtained before first composite number appears.

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

Offset

1,7

Comments

If n itself is a prime, it is not included in the count. - Antti Karttunen, Feb 13 2019

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

P. De Geest, World!Of Palindromic Primes

Example

1 -> 11 (prime) -> 21 (composite), so a(1) = 1.

Prog

(PARI)
A045918(a) = { my(c=1); for(j=2, #a=Vec(Str(a)), if(a[j-1]==a[j], a[j-1]=""; c++, a[j-1]=Str(c, a[j-1]); c=1)); a[#a]=Str(c, a[#a]); eval(concat(a)) }; \\ From A045918 by M. F. Hasler, Jan 27 2012
A037047(n) = if(1==n, n, my(c=0); while(1, n = A045918(n); if(isprime(n), c++, return(c)))); \\ Antti Karttunen, Feb 13 2019

Crossrefs

Cf. A005150, A036978, A045918.

Sequence in context: A353373 A064530 A307832 * A118917 A325045 A204293

Adjacent sequences: A037044 A037045 A037046 * A037048 A037049 A037050

Keyword

nonn,base

Author

G. L. Honaker, Jr.

Extensions

More terms from Antti Karttunen, Feb 13 2019

Status

approved