A100963 -id:A100963 - cp's OEIS frontend

A255260 a(n) = a(n-1) + sum of the pentagonal numbers which are among the first (n-1) terms of the sequence, with a(1)=1.

1, 2, 3, 4, 5, 11, 17, 23, 29, 35, 76, 117, 275, 433, 591, 749, 907, 1065, 1223, 1381, 1539, 1697, 1855, 2013, 2171, 2329, 2487, 2645, 2803, 2961, 3119, 3277, 3435, 3593, 3751, 3909, 4067, 4225, 4383, 4541, 4699, 4857, 5015, 5173, 5331, 5489, 5647, 5805

Offset: 1

Colin Barker, Feb 19 2015

nonn

			a(7) = 17 because a(6) = 11, pentagonal numbers already in the sequence are 1 and 5, and 11+1+5 = 17.

Colin Barker, Table of n, a(n) for n = 1..1000

Cf. A100963, A101135, A255261.

vector(100, n, if(n==1, a_n_1=sum_=1, a_n_1+=sum_; if(ispolygonal(a_n_1, 5), sum_+=a_n_1)); a_n_1)

A255261 a(n) = a(n-1) + sum of the hexagonal numbers which are among the first (n-1) terms of the sequence, with a(1)=1.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 13, 20, 27, 34, 41, 48, 55, 62, 69, 76, 83, 90, 97, 104, 111, 118, 125, 132, 139, 146, 153, 313, 473, 633, 793, 953, 1113, 1273, 1433, 1593, 1753, 1913, 2073, 2233, 2393, 2553, 2713, 2873, 3033, 3193, 3353, 3513, 3673, 3833, 3993, 4153

Offset: 1

Colin Barker, Feb 20 2015

nonn

			a(8) = 20 because a(7) = 13, hexagonal numbers already in the sequence are 1 and 6, and 13+1+6 = 20.

Colin Barker, Table of n, a(n) for n = 1..1000

Cf. A100963, A101135, A255260.

vector(100, n, if(n==1, a_n_1=sum_=1, a_n_1+=sum_; if(ispolygonal(a_n_1, 6), sum_+=a_n_1)); a_n_1)

cp's OEIS Frontend

A255260 a(n) = a(n-1) + sum of the pentagonal numbers which are among the first (n-1) terms of the sequence, with a(1)=1.

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