A158862 - OEIS

A158862

Numbers k such that prepending 3 to the k-th triangular number produces a prime.

22, 46, 61, 82, 106, 118, 181, 286, 301, 373, 406, 433, 481, 493, 526, 562, 577, 661, 733, 802, 817, 886, 946, 961, 1033, 1162, 1177, 1246, 1258, 1261, 1297, 1342, 1426, 1513, 1546, 1558, 1573, 1618, 1741, 1813, 1822, 1846, 1873, 1882, 1918, 1921, 1957

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OFFSET

1,1

COMMENTS

Or, concatenated T(2) and T(k) are prime. Or, concatenated A000217(2) and A000217(k) are prime.

LINKS

Table of n, a(n) for n=1..47.

EXAMPLE

T(2)=253, 3253 is prime, so 22 is a term;

T(46)=1081, 31081 is prime, so 46 is a term;

T(61)=1891, 31891 is prime, so 61 is a term.

CROSSREFS