A147846 - OEIS

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A147846

Triangular numbers n*(n+1)/2 with n or n+1 prime.

1, 3, 6, 10, 15, 21, 28, 55, 66, 78, 91, 136, 153, 171, 190, 253, 276, 406, 435, 465, 496, 666, 703, 820, 861, 903, 946, 1081, 1128, 1378, 1431, 1711, 1770, 1830, 1891, 2211, 2278, 2485, 2556, 2628, 2701, 3081, 3160, 3403, 3486, 3916, 4005, 4656, 4753, 5050

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ (n^2 log^2 n)/8. - Charles R Greathouse IV, Jun 03 2013

PROG

(PARI) lista(nn) = {for (n=1, nn, if (isprime(n) || isprime(n+1), print1(n*(n+1)/2, ", ")); ); } \\ Michel Marcus, Jun 03 2013

(PARI) print1(1); forprime(p=3, 7, print1(", "p*(p-1)/2", "p*(p+1)/2)) \\ Charles R Greathouse IV, Jun 03 2013

CROSSREFS

Cf. A000217.