A043347 To form the sequence, write the primes 2, 3, 5, 7,... as an infinite string 2357111317...; then take the first 2 digits of the string, 23, then the next 3 digits, 571, then the next 5 digits, 11317, then the next 7 digits, 1923293, then... (stepping through prime numbers of digits). Omit any leading 0's.

23, 571, 11317, 1923293, 13741434753, 5961677173798, 38997101103107109, 1131271311371391491, 51157163167173179181191, 19319719921122322722923323924, 1251257263269271277281283293307, 3113133173313373473493533593673733793, 83389397401409419421431433439443449457461

Offset

1,1

Comments

The first four terms of the sequence are primes - see A066776.

a(169) has 1009 digits. - Michael S. Branicky, Dec 30 2025

Links

Michael S. Branicky, Table of n, a(n) for n = 1..168

Mathematica

a[n_] := (k = Prime[ Floor[n^(3/2)]] + 6; l = Sum[ Prime[i], {i, 1, n - 1} ]; b = ""; Do[ b = StringJoin[b, ToString[ Prime[i]]], {i, 1, k} ]; Return[ ToExpression[ StringTake[ StringDrop[b, l], Prime[n]]]]); Table[ a[n], {n, 1, 13} ]

Prog

(Python)
from sympy import nextprime
from itertools import islice
def A043347(): # generator of terms
    p, q, s = 2, 2, ""
    while True:
        while len(s) < p:
            s += str(q)
            q = nextprime(q)
        yield int(s[:p])
        p, s = nextprime(p), s[p:]
print(list(islice(A043347(), 13))) # Michael S. Branicky, Dec 30 2025

Crossrefs

Cf. A000040, A059932, A066776.

Sequence in context: A196536 A231261 A242358 * A015696 A106538 A203102

Adjacent sequences: A043344 A043345 A043346 * A043348 A043349 A043350

Keyword

nonn,base

Author

Joseph L. Pe, Jan 12 2002

Extensions

More terms from Robert G. Wilson v, Jan 16 2002

a(12) onward from Michael S. Branicky, Dec 30 2025

Status

approved