OFFSET
1,1
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
Patrick De Geest, Home Primes
EXAMPLE
698 is in the sequence as 698 -> 2349 -> 333329 -> 2571297 -> 3857099 -> 31312323 -> 33771937101 -> 379437170413 -> 73124171910091 -> 374148203145623. Only after the ninth iteration we reach a prime. - David A. Corneth, Oct 15 2019
PROG
(PARI) is(n, k) = if(isprime(n), return(0)); for(i = 1, k - 1, n = concatelements(primesvector(n)); if(isprime(n), return(0))); n = concatelements(primesvector(n)); isprime(n)
concatelements(v) = my(s = ""); for(i = 1, #v, s = concat(s, v[i])); eval(s)
primesvector(n) = my(f = factor(n), res = vector(vecsum(f[, 2])), t = 0); for(i = 1, #f~, for(j = 1, f[i, 2], t++; res[t] = f[i, 1])); res \\ David A. Corneth, Oct 15 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Jun 15 1998
EXTENSIONS
Extended and edited by Charles R Greathouse IV, Apr 28 2010
STATUS
approved