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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A046429 Numbers requiring 9 steps to reach a prime under the prime factor concatenation procedure. 1
 40, 44, 81, 224, 265, 395, 422, 462, 640, 698, 818, 972, 1010, 1032, 1070, 1089, 1174, 1206, 1280, 1336, 1446, 1518, 1520, 1528, 1581, 1662, 1728, 1814, 1816, 1849, 1852, 1853, 1856, 1892, 1927, 1932, 1960, 2032, 2060, 2061, 2090, 2098, 2202, 2212, 2249 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A037271, A046411. Sequence in context: A095513 A095505 A095497 * A046796 A333712 A204746 Adjacent sequences:  A046426 A046427 A046428 * A046430 A046431 A046432 KEYWORD nonn,base AUTHOR Patrick De Geest, Jun 15 1998 EXTENSIONS Extended and edited by Charles R Greathouse IV, Apr 28 2010 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 August 1 14:44 EDT 2021. Contains 346393 sequences. (Running on oeis4.)