OFFSET
1,2
COMMENTS
Comments from N. J. A. Sloane, Dec 07 2019: (Start)
Eric Angelini and Kay Rosen suggest these could be called Pnuumlde numbers.
Eric Angelini asks if any term is a prime.
James R. Buddenhagen finds that the first prime is a(121), a 255-digit prime according to Maple.
Hans Havermann finds that there is one more prime in the first 10000 terms, a(1399), which is a 4489-digit prime.
(End)
The third prime in the sequence is a(40714) with 192464 decimal digits. The terms at even indices are duplicated by the even-indexed terms of A281254, which is why this term is a prime for both sequences. - Hans Havermann, Jan 16 2020
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..369
Felice Russo, A set of new Smarandache functions, sequences and conjectures in number theory, American Research Press 2000.
MATHEMATICA
nxt[{n_, a_}]:={n+1, If[OddQ[n], (n+1)*10^IntegerLength[a]+a, a*10^IntegerLength[ n+1]+ n+1]}; NestList[nxt, {1, 1}, 30][[All, 2]] (* Harvey P. Dale, Jul 20 2022 *)
PROG
(PARI) lista(nn) = {print1(val=1, ", "); b = 0; for (n=2, nn, if (b, val = concat(Str(val), Str(n)), val = concat(Str(n), Str(val))); print1(val, ", "); b = 1 - b; ); } \\ Michel Marcus, Aug 11 2017
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Felice Russo, Feb 25 2000
EXTENSIONS
More terms from Michel Marcus, Aug 11 2017
STATUS
approved